web/html/docs/security-guide/en_US/Common_Content/css - New directory
by Eric Christensen
Author: sparks
Update of /cvs/fedora/web/html/docs/security-guide/en_US/Common_Content/css
In directory cvs1.fedora.phx.redhat.com:/tmp/cvs-serv29170/css
Log Message:
Directory /cvs/fedora/web/html/docs/security-guide/en_US/Common_Content/css added to the repository
14 years, 9 months
- 1
- 0
web/html/docs/security-guide/en_US/images - New directory
by Eric Christensen
Author: sparks
Update of /cvs/fedora/web/html/docs/security-guide/en_US/images
In directory cvs1.fedora.phx.redhat.com:/tmp/cvs-serv27427/images
Log Message:
Directory /cvs/fedora/web/html/docs/security-guide/en_US/images added to the repository
14 years, 9 months
- 1
- 0
web/html/docs/security-guide/en_US/Common_Content - New directory
by Eric Christensen
Author: sparks
Update of /cvs/fedora/web/html/docs/security-guide/en_US/Common_Content
In directory cvs1.fedora.phx.redhat.com:/tmp/cvs-serv27320/Common_Content
Log Message:
Directory /cvs/fedora/web/html/docs/security-guide/en_US/Common_Content added to the repository
14 years, 9 months
- 1
- 0
web/html/docs/security-guide/en_US Security_Guide-Encryption-Data_in_Motion-Secure_Shell.php, 1.1, NONE Security_Guide-Encryption-Data_in_Motion-Virtual_Private_Networks.php, 1.1, NONE Security_Guide-Encryption-Data_in_Motion.php, 1.1, NONE Security_Guide-Encryption-Protecting_Data_at_Rest-File_Based_Encryption.php, 1.1, NONE We_Need_Feedback.php, 1.1, NONE chap-Security_Guide-Encryption.php, 1.1, NONE chap-Security_Guide-General_Principles_of_Information_Security.php, 1.1, NONE chap-Security_Guide-LUKS_Dis
by Karsten Wade
Author: kwade
Update of /cvs/fedora/web/html/docs/security-guide/en_US
In directory cvs1.fedora.phx.redhat.com:/tmp/cvs-serv26290
Removed Files:
Security_Guide-Encryption-Data_in_Motion-Secure_Shell.php
Security_Guide-Encryption-Data_in_Motion-Virtual_Private_Networks.php
Security_Guide-Encryption-Data_in_Motion.php
Security_Guide-Encryption-Protecting_Data_at_Rest-File_Based_Encryption.php
We_Need_Feedback.php chap-Security_Guide-Encryption.php
chap-Security_Guide-General_Principles_of_Information_Security.php
chap-Security_Guide-LUKS_Disk_Encryption.php
chap-Security_Guide-References.php
chap-Security_Guide-Secure_Installation.php
chap-Security_Guide-Securing_Your_Network.php
chap-Security_Guide-Security_Overview.php
chap-Security_Guide-Software_Maintenance.php index.php
pref-Security_Guide-Preface.php
sect-Security_Guide-Additional_Resources-Related_Books.php
sect-Security_Guide-Additional_Resources-Related_Documentation.php
sect-Security_Guide-Additional_Resources-Useful_Firewall_Websites.php
sect-Security_Guide-Additional_Resources-Useful_IP_Tables_Websites.php
sect-Security_Guide-Additional_Resources-Useful_Kerberos_Websites.php
sect-Security_Guide-Additional_Resources-Useful_PAM_Websites.php
sect-Security_Guide-Additional_Resources-Useful_TCP_Wrappers_Websites.php
sect-Security_Guide-Altering_xinetd_Configuration_Files-Access_Control_Options.php
sect-Security_Guide-Altering_xinetd_Configuration_Files-Binding_and_Redirection_Options.php
sect-Security_Guide-Altering_xinetd_Configuration_Files-Resource_Management_Options.php
sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Network_Security.php
sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Server_Security.php
sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Workstation_and_Home_PC_Security.php
sect-Security_Guide-Attackers_and_Vulnerabilities.php
sect-Security_Guide-Basic_Firewall_Configuration-Activating_the_IPTables_Service.php
sect-Security_Guide-Basic_Firewall_Configuration-Enabling_and_Disabling_the_Firewall.php
sect-Security_Guide-Basic_Firewall_Configuration-Other_Ports.php
sect-Security_Guide-Basic_Firewall_Configuration-Saving_the_Settings.php
sect-Security_Guide-Basic_Firewall_Configuration-Trusted_Services.php
sect-Security_Guide-Command_Options_for_IPTables-Command_Options.php
sect-Security_Guide-Command_Options_for_IPTables-IPTables_Match_Options.php
sect-Security_Guide-Command_Options_for_IPTables-IPTables_Parameter_Options.php
sect-Security_Guide-Command_Options_for_IPTables-Listing_Options.php
sect-Security_Guide-Command_Options_for_IPTables-Target_Options.php
sect-Security_Guide-Common_Exploits_and_Attacks.php
sect-Security_Guide-Encryption-Protecting_Data_at_Rest-Full_Disk_Encryption.php
sect-Security_Guide-Evaluating_the_Tools-Anticipating_Your_Future_Needs.php
sect-Security_Guide-Evaluating_the_Tools-Nessus.php
sect-Security_Guide-Evaluating_the_Tools-Nikto.php
sect-Security_Guide-Evaluating_the_Tools-VLAD_the_Scanner.php
sect-Security_Guide-FORWARD_and_NAT_Rules-DMZs_and_IPTables.php
sect-Security_Guide-FORWARD_and_NAT_Rules-Prerouting.php
sect-Security_Guide-Firewalls-Additional_Resources.php
sect-Security_Guide-Firewalls-Basic_Firewall_Configuration.php
sect-Security_Guide-Firewalls-Common_IPTables_Filtering.php
sect-Security_Guide-Firewalls-FORWARD_and_NAT_Rules.php
sect-Security_Guide-Firewalls-IPTables_and_Connection_Tracking.php
sect-Security_Guide-Firewalls-IPv6.php
sect-Security_Guide-Firewalls-Malicious_Software_and_Spoofed_IP_Addresses.php
sect-Security_Guide-Firewalls-Using_IPTables.php
sect-Security_Guide-Firewalls.php
sect-Security_Guide-General_Principles_of_Information_Security-DISA_IASE_Documents.php
sect-Security_Guide-General_Principles_of_Information_Security-NSA_Documents.php
sect-Security_Guide-General_Principles_of_Information_Security-Tips_Guides_and_Tools.php
sect-Security_Guide-IPTables-Additional_Resources.php
sect-Security_Guide-IPTables-Command_Options_for_IPTables.php
sect-Security_Guide-IPTables-Differences_Between_IPTables_and_IPChains.php
sect-Security_Guide-IPTables-IPTables_Control_Scripts.php
sect-Security_Guide-IPTables-IPTables_and_IPv6.php
sect-Security_Guide-IPTables-Saving_IPTables_Rules.php
sect-Security_Guide-IPTables.php
sect-Security_Guide-IPTables_Match_Options-Additional_Match_Option_Modules.php
sect-Security_Guide-IPTables_Match_Options-ICMP_Protocol.php
sect-Security_Guide-IPTables_Match_Options-UDP_Protocol.php
sect-Security_Guide-IPsec_Host_to_Host_Configuration-Manual_IPsec_Host_to_Host_Configuration.php
sect-Security_Guide-IPsec_Network_to_Network_Configuration-Manual_IPsec_Network_to_Network_Configuration.php
sect-Security_Guide-Kerberos-Additional_Resources.php
sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Client.php
sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Server.php
sect-Security_Guide-Kerberos-Domain_to_Realm_Mapping.php
sect-Security_Guide-Kerberos-How_Kerberos_Works.php
sect-Security_Guide-Kerberos-Kerberos_Terminology.php
sect-Security_Guide-Kerberos-Kerberos_and_PAM.php
sect-Security_Guide-Kerberos-Setting_Up_Cross_Realm_Authentication.php
sect-Security_Guide-Kerberos-Setting_Up_Secondary_KDCs.php
sect-Security_Guide-Kerberos.php
sect-Security_Guide-LUKS_Disk_Encryption-Links_of_Interest.php
sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-Step_by_Step_Instructions.php
sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-What_you_have_just_accomplished.php
sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories.php
sect-Security_Guide-Option_Fields-Access_Control.php
sect-Security_Guide-Option_Fields-Expansions.php
sect-Security_Guide-Option_Fields-Shell_Commands.php
sect-Security_Guide-PAM_Configuration_File_Format-Control_Flag.php
sect-Security_Guide-PAM_Configuration_File_Format-Module_Arguments.php
sect-Security_Guide-PAM_Configuration_File_Format-Module_Name.php
sect-Security_Guide-PAM_and_Administrative_Credential_Caching-Common_pam_timestamp_Directives.php
sect-Security_Guide-PAM_and_Device_Ownership-Application_Access.php
sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Additional_Resources.php
sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Creating_PAM_Modules.php
sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_Configuration_File_Format.php
sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_Configuration_Files.php
sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Administrative_Credential_Caching.php
sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Device_Ownership.php
sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Sample_PAM_Configuration_Files.php
sect-Security_Guide-Pluggable_Authentication_Modules_PAM.php
sect-Security_Guide-Secure_Installation-Utilize_LUKS_Partition_Encryption.php
sect-Security_Guide-Securing_FTP-Anonymous_Access.php
sect-Security_Guide-Securing_FTP-Use_TCP_Wrappers_To_Control_Access.php
sect-Security_Guide-Securing_FTP-User_Accounts.php
sect-Security_Guide-Securing_NFS-Beware_of_Syntax_Errors.php
sect-Security_Guide-Securing_NFS-Do_Not_Use_the_no_root_squash_Option.php
sect-Security_Guide-Securing_NIS-Assign_Static_Ports_and_Use_iptables_Rules.php
sect-Security_Guide-Securing_NIS-Edit_the_varypsecurenets_File.php
sect-Security_Guide-Securing_NIS-Use_Kerberos_Authentication.php
sect-Security_Guide-Securing_NIS-Use_a_Password_like_NIS_Domain_Name_and_Hostname.php
sect-Security_Guide-Securing_Portmap-Protect_portmap_With_iptables.php
sect-Security_Guide-Securing_Sendmail-Mail_only_Users.php
sect-Security_Guide-Securing_Sendmail-NFS_and_Sendmail.php
sect-Security_Guide-Securing_the_Apache_HTTP_Server-Do_Not_Remove_the_IncludesNoExec_Directive.php
sect-Security_Guide-Securing_the_Apache_HTTP_Server-Restrict_Permissions_for_Executable_Directories.php
sect-Security_Guide-Securing_the_Apache_HTTP_Server-The_Indexes_Directive.php
sect-Security_Guide-Securing_the_Apache_HTTP_Server-The_UserDir_Directive.php
sect-Security_Guide-Security_Updates.php
sect-Security_Guide-Server_Security-Securing_FTP.php
sect-Security_Guide-Server_Security-Securing_NFS.php
sect-Security_Guide-Server_Security-Securing_NIS.php
sect-Security_Guide-Server_Security-Securing_Portmap.php
sect-Security_Guide-Server_Security-Securing_Sendmail.php
sect-Security_Guide-Server_Security-Securing_the_Apache_HTTP_Server.php
sect-Security_Guide-Server_Security-Verifying_Which_Ports_Are_Listening.php
sect-Security_Guide-Server_Security.php
sect-Security_Guide-Single_Sign_on_SSO-Configuring_Firefox_to_use_Kerberos_for_SSO.php
sect-Security_Guide-Single_Sign_on_SSO-Getting_Started_with_your_new_Smart_Card.php
sect-Security_Guide-Single_Sign_on_SSO-How_Smart_Card_Enrollment_Works.php
sect-Security_Guide-Single_Sign_on_SSO-How_Smart_Card_Login_Works.php
sect-Security_Guide-Single_Sign_on_SSO.php
sect-Security_Guide-Software_Maintenance-Install_Signed_Packages_from_Well_Known_Repositories.php
sect-Security_Guide-Software_Maintenance-Plan_and_Configure_Security_Updates-Adjusting_Automatic_Updates.php
sect-Security_Guide-Software_Maintenance-Plan_and_Configure_Security_Updates.php
sect-Security_Guide-TCP_Wrappers_Configuration_Files-Option_Fields.php
sect-Security_Guide-TCP_Wrappers_and_xinetd-Additional_Resources.php
sect-Security_Guide-TCP_Wrappers_and_xinetd-TCP_Wrappers_Configuration_Files.php
sect-Security_Guide-TCP_Wrappers_and_xinetd-xinetd.php
sect-Security_Guide-TCP_Wrappers_and_xinetd-xinetd_Configuration_Files.php
sect-Security_Guide-TCP_Wrappers_and_xinetd.php
sect-Security_Guide-Threats_to_Server_Security-Inattentive_Administration.php
sect-Security_Guide-Threats_to_Server_Security-Inherently_Insecure_Services.php
sect-Security_Guide-Threats_to_Server_Security-Unpatched_Services.php
sect-Security_Guide-Threats_to_Workstation_and_Home_PC_Security-Vulnerable_Client_Applications.php
sect-Security_Guide-Using_IPTables-Basic_Firewall_Policies.php
sect-Security_Guide-Using_IPTables-Saving_and_Restoring_IPTables_Rules.php
sect-Security_Guide-Virtual_Private_Networks_VPNs-Creating_an_IPsec_Connection.php
sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec.php
sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec_Host_to_Host_Configuration.php
sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec_Installation.php
sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec_Network_to_Network_Configuration.php
sect-Security_Guide-Virtual_Private_Networks_VPNs-Starting_and_Stopping_an_IPsec_Connection.php
sect-Security_Guide-Virtual_Private_Networks_VPNs-VPNs_and_PROD.php
sect-Security_Guide-Virtual_Private_Networks_VPNs.php
sect-Security_Guide-Vulnerability_Assessment-Defining_Assessment_and_Testing.php
sect-Security_Guide-Vulnerability_Assessment-Evaluating_the_Tools.php
sect-Security_Guide-Vulnerability_Assessment.php
sect-Security_Guide-xinetd_Configuration_Files-Altering_xinetd_Configuration_Files.php
sect-Security_Guide-xinetd_Configuration_Files-The_etcxinetd.d_Directory.php
Log Message:
removing the PHP files so we are only using the HTML and not confusing the web server :)
--- Security_Guide-Encryption-Data_in_Motion-Secure_Shell.php DELETED ---
--- Security_Guide-Encryption-Data_in_Motion-Virtual_Private_Networks.php DELETED ---
--- Security_Guide-Encryption-Data_in_Motion.php DELETED ---
--- Security_Guide-Encryption-Protecting_Data_at_Rest-File_Based_Encryption.php DELETED ---
--- We_Need_Feedback.php DELETED ---
--- chap-Security_Guide-Encryption.php DELETED ---
--- chap-Security_Guide-General_Principles_of_Information_Security.php DELETED ---
--- chap-Security_Guide-LUKS_Disk_Encryption.php DELETED ---
--- chap-Security_Guide-References.php DELETED ---
--- chap-Security_Guide-Secure_Installation.php DELETED ---
--- chap-Security_Guide-Securing_Your_Network.php DELETED ---
--- chap-Security_Guide-Security_Overview.php DELETED ---
--- chap-Security_Guide-Software_Maintenance.php DELETED ---
--- index.php DELETED ---
--- pref-Security_Guide-Preface.php DELETED ---
--- sect-Security_Guide-Additional_Resources-Related_Books.php DELETED ---
--- sect-Security_Guide-Additional_Resources-Related_Documentation.php DELETED ---
--- sect-Security_Guide-Additional_Resources-Useful_Firewall_Websites.php DELETED ---
--- sect-Security_Guide-Additional_Resources-Useful_IP_Tables_Websites.php DELETED ---
--- sect-Security_Guide-Additional_Resources-Useful_Kerberos_Websites.php DELETED ---
--- sect-Security_Guide-Additional_Resources-Useful_PAM_Websites.php DELETED ---
--- sect-Security_Guide-Additional_Resources-Useful_TCP_Wrappers_Websites.php DELETED ---
--- sect-Security_Guide-Altering_xinetd_Configuration_Files-Access_Control_Options.php DELETED ---
--- sect-Security_Guide-Altering_xinetd_Configuration_Files-Binding_and_Redirection_Options.php DELETED ---
--- sect-Security_Guide-Altering_xinetd_Configuration_Files-Resource_Management_Options.php DELETED ---
--- sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Network_Security.php DELETED ---
--- sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Server_Security.php DELETED ---
--- sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Workstation_and_Home_PC_Security.php DELETED ---
--- sect-Security_Guide-Attackers_and_Vulnerabilities.php DELETED ---
--- sect-Security_Guide-Basic_Firewall_Configuration-Activating_the_IPTables_Service.php DELETED ---
--- sect-Security_Guide-Basic_Firewall_Configuration-Enabling_and_Disabling_the_Firewall.php DELETED ---
--- sect-Security_Guide-Basic_Firewall_Configuration-Other_Ports.php DELETED ---
--- sect-Security_Guide-Basic_Firewall_Configuration-Saving_the_Settings.php DELETED ---
--- sect-Security_Guide-Basic_Firewall_Configuration-Trusted_Services.php DELETED ---
--- sect-Security_Guide-Command_Options_for_IPTables-Command_Options.php DELETED ---
--- sect-Security_Guide-Command_Options_for_IPTables-IPTables_Match_Options.php DELETED ---
--- sect-Security_Guide-Command_Options_for_IPTables-IPTables_Parameter_Options.php DELETED ---
--- sect-Security_Guide-Command_Options_for_IPTables-Listing_Options.php DELETED ---
--- sect-Security_Guide-Command_Options_for_IPTables-Target_Options.php DELETED ---
--- sect-Security_Guide-Common_Exploits_and_Attacks.php DELETED ---
--- sect-Security_Guide-Encryption-Protecting_Data_at_Rest-Full_Disk_Encryption.php DELETED ---
--- sect-Security_Guide-Evaluating_the_Tools-Anticipating_Your_Future_Needs.php DELETED ---
--- sect-Security_Guide-Evaluating_the_Tools-Nessus.php DELETED ---
--- sect-Security_Guide-Evaluating_the_Tools-Nikto.php DELETED ---
--- sect-Security_Guide-Evaluating_the_Tools-VLAD_the_Scanner.php DELETED ---
--- sect-Security_Guide-FORWARD_and_NAT_Rules-DMZs_and_IPTables.php DELETED ---
--- sect-Security_Guide-FORWARD_and_NAT_Rules-Prerouting.php DELETED ---
--- sect-Security_Guide-Firewalls-Additional_Resources.php DELETED ---
--- sect-Security_Guide-Firewalls-Basic_Firewall_Configuration.php DELETED ---
--- sect-Security_Guide-Firewalls-Common_IPTables_Filtering.php DELETED ---
--- sect-Security_Guide-Firewalls-FORWARD_and_NAT_Rules.php DELETED ---
--- sect-Security_Guide-Firewalls-IPTables_and_Connection_Tracking.php DELETED ---
--- sect-Security_Guide-Firewalls-IPv6.php DELETED ---
--- sect-Security_Guide-Firewalls-Malicious_Software_and_Spoofed_IP_Addresses.php DELETED ---
--- sect-Security_Guide-Firewalls-Using_IPTables.php DELETED ---
--- sect-Security_Guide-Firewalls.php DELETED ---
--- sect-Security_Guide-General_Principles_of_Information_Security-DISA_IASE_Documents.php DELETED ---
--- sect-Security_Guide-General_Principles_of_Information_Security-NSA_Documents.php DELETED ---
--- sect-Security_Guide-General_Principles_of_Information_Security-Tips_Guides_and_Tools.php DELETED ---
--- sect-Security_Guide-IPTables-Additional_Resources.php DELETED ---
--- sect-Security_Guide-IPTables-Command_Options_for_IPTables.php DELETED ---
--- sect-Security_Guide-IPTables-Differences_Between_IPTables_and_IPChains.php DELETED ---
--- sect-Security_Guide-IPTables-IPTables_Control_Scripts.php DELETED ---
--- sect-Security_Guide-IPTables-IPTables_and_IPv6.php DELETED ---
--- sect-Security_Guide-IPTables-Saving_IPTables_Rules.php DELETED ---
--- sect-Security_Guide-IPTables.php DELETED ---
--- sect-Security_Guide-IPTables_Match_Options-Additional_Match_Option_Modules.php DELETED ---
--- sect-Security_Guide-IPTables_Match_Options-ICMP_Protocol.php DELETED ---
--- sect-Security_Guide-IPTables_Match_Options-UDP_Protocol.php DELETED ---
--- sect-Security_Guide-IPsec_Host_to_Host_Configuration-Manual_IPsec_Host_to_Host_Configuration.php DELETED ---
--- sect-Security_Guide-IPsec_Network_to_Network_Configuration-Manual_IPsec_Network_to_Network_Configuration.php DELETED ---
--- sect-Security_Guide-Kerberos-Additional_Resources.php DELETED ---
--- sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Client.php DELETED ---
--- sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Server.php DELETED ---
--- sect-Security_Guide-Kerberos-Domain_to_Realm_Mapping.php DELETED ---
--- sect-Security_Guide-Kerberos-How_Kerberos_Works.php DELETED ---
--- sect-Security_Guide-Kerberos-Kerberos_Terminology.php DELETED ---
--- sect-Security_Guide-Kerberos-Kerberos_and_PAM.php DELETED ---
--- sect-Security_Guide-Kerberos-Setting_Up_Cross_Realm_Authentication.php DELETED ---
--- sect-Security_Guide-Kerberos-Setting_Up_Secondary_KDCs.php DELETED ---
--- sect-Security_Guide-Kerberos.php DELETED ---
--- sect-Security_Guide-LUKS_Disk_Encryption-Links_of_Interest.php DELETED ---
--- sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-Step_by_Step_Instructions.php DELETED ---
--- sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-What_you_have_just_accomplished.php DELETED ---
--- sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories.php DELETED ---
--- sect-Security_Guide-Option_Fields-Access_Control.php DELETED ---
--- sect-Security_Guide-Option_Fields-Expansions.php DELETED ---
--- sect-Security_Guide-Option_Fields-Shell_Commands.php DELETED ---
--- sect-Security_Guide-PAM_Configuration_File_Format-Control_Flag.php DELETED ---
--- sect-Security_Guide-PAM_Configuration_File_Format-Module_Arguments.php DELETED ---
--- sect-Security_Guide-PAM_Configuration_File_Format-Module_Name.php DELETED ---
--- sect-Security_Guide-PAM_and_Administrative_Credential_Caching-Common_pam_timestamp_Directives.php DELETED ---
--- sect-Security_Guide-PAM_and_Device_Ownership-Application_Access.php DELETED ---
--- sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Additional_Resources.php DELETED ---
--- sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Creating_PAM_Modules.php DELETED ---
--- sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_Configuration_File_Format.php DELETED ---
--- sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_Configuration_Files.php DELETED ---
--- sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Administrative_Credential_Caching.php DELETED ---
--- sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Device_Ownership.php DELETED ---
--- sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Sample_PAM_Configuration_Files.php DELETED ---
--- sect-Security_Guide-Pluggable_Authentication_Modules_PAM.php DELETED ---
--- sect-Security_Guide-Secure_Installation-Utilize_LUKS_Partition_Encryption.php DELETED ---
--- sect-Security_Guide-Securing_FTP-Anonymous_Access.php DELETED ---
--- sect-Security_Guide-Securing_FTP-Use_TCP_Wrappers_To_Control_Access.php DELETED ---
--- sect-Security_Guide-Securing_FTP-User_Accounts.php DELETED ---
--- sect-Security_Guide-Securing_NFS-Beware_of_Syntax_Errors.php DELETED ---
--- sect-Security_Guide-Securing_NFS-Do_Not_Use_the_no_root_squash_Option.php DELETED ---
--- sect-Security_Guide-Securing_NIS-Assign_Static_Ports_and_Use_iptables_Rules.php DELETED ---
--- sect-Security_Guide-Securing_NIS-Edit_the_varypsecurenets_File.php DELETED ---
--- sect-Security_Guide-Securing_NIS-Use_Kerberos_Authentication.php DELETED ---
--- sect-Security_Guide-Securing_NIS-Use_a_Password_like_NIS_Domain_Name_and_Hostname.php DELETED ---
--- sect-Security_Guide-Securing_Portmap-Protect_portmap_With_iptables.php DELETED ---
--- sect-Security_Guide-Securing_Sendmail-Mail_only_Users.php DELETED ---
--- sect-Security_Guide-Securing_Sendmail-NFS_and_Sendmail.php DELETED ---
--- sect-Security_Guide-Securing_the_Apache_HTTP_Server-Do_Not_Remove_the_IncludesNoExec_Directive.php DELETED ---
--- sect-Security_Guide-Securing_the_Apache_HTTP_Server-Restrict_Permissions_for_Executable_Directories.php DELETED ---
--- sect-Security_Guide-Securing_the_Apache_HTTP_Server-The_Indexes_Directive.php DELETED ---
--- sect-Security_Guide-Securing_the_Apache_HTTP_Server-The_UserDir_Directive.php DELETED ---
--- sect-Security_Guide-Security_Updates.php DELETED ---
--- sect-Security_Guide-Server_Security-Securing_FTP.php DELETED ---
--- sect-Security_Guide-Server_Security-Securing_NFS.php DELETED ---
--- sect-Security_Guide-Server_Security-Securing_NIS.php DELETED ---
--- sect-Security_Guide-Server_Security-Securing_Portmap.php DELETED ---
--- sect-Security_Guide-Server_Security-Securing_Sendmail.php DELETED ---
--- sect-Security_Guide-Server_Security-Securing_the_Apache_HTTP_Server.php DELETED ---
--- sect-Security_Guide-Server_Security-Verifying_Which_Ports_Are_Listening.php DELETED ---
--- sect-Security_Guide-Server_Security.php DELETED ---
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14 years, 9 months
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web/html/docs/security-guide/en_US Security_Guide-Encryption-Data_in_Motion-Secure_Shell.html, NONE, 1.1 Security_Guide-Encryption-Data_in_Motion-Virtual_Private_Networks.html, NONE, 1.1 Security_Guide-Encryption-Data_in_Motion.html, NONE, 1.1 Security_Guide-Encryption-Protecting_Data_at_Rest-File_Based_Encryption.html, NONE, 1.1 We_Need_Feedback.html, NONE, 1.1 chap-Security_Guide-Encryption.html, NONE, 1.1 chap-Security_Guide-General_Principles_of_Information_Security.html, NONE, 1.1 chap-Security_Guide-R
by Eric Christensen
Author: sparks
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In directory cvs1.fedora.phx.redhat.com:/tmp/cvs-serv8959
Added Files:
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Security_Guide-Encryption-Data_in_Motion-Virtual_Private_Networks.html
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sect-Security_Guide-Virtual_Private_Networks_VPNs.html
sect-Security_Guide-Vulnerability_Assessment-Defining_Assessment_and_Testing.html
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sect-Security_Guide-xinetd_Configuration_Files-The_etcxinetd.d_Directory.html
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--- NEW FILE Security_Guide-Encryption-Data_in_Motion-Secure_Shell.html ---
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>3.6. Secure Shell</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="chap-Security_Guide-Encryption.html" title="Chapter 3. Encryption"/><link rel="prev" href="Security_Guide-Encryption-Data_in_Motion-Virtual_Private_Networks.html" title="3.5. Virtual Private Networks"/><link rel="next" href="sect-Security_Guide-LUKS_Disk_Encryption.html" title="3.7. LUKS Disk Encryption"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li cl
ass="previous"><a accesskey="p" href="Security_Guide-Encryption-Data_in_Motion-Virtual_Private_Networks.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-LUKS_Disk_Encryption.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="Security_Guide-Encryption-Data_in_Motion-Secure_Shell">3.6. Secure Shell</h2></div></div></div><div class="para">
Secure Shell (SSH) also provides encrypted tunnels between computers but only using a single port. <a href="http://www.redhatmagazine.com/2007/11/27/advanced-ssh-configuration-and-t...">Port forwarding can be done over an SSH tunnel</a> and traffic will be encrypted as it passes over that tunnel but using port forwarding isn't as fluid as a VPN.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="Security_Guide-Encryption-Data_in_Motion-Virtual_Private_Networks.html"><strong>Prev</strong>3.5. Virtual Private Networks</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-LUKS_Disk_Encryption.html"><strong>Next</strong>3.7. LUKS Disk Encryption</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>3.5. Virtual Private Networks</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="chap-Security_Guide-Encryption.html" title="Chapter 3. Encryption"/><link rel="prev" href="Security_Guide-Encryption-Data_in_Motion.html" title="3.4. Data in Motion"/><link rel="next" href="Security_Guide-Encryption-Data_in_Motion-Secure_Shell.html" title="3.6. Secure Shell"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a
accesskey="p" href="Security_Guide-Encryption-Data_in_Motion.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="Security_Guide-Encryption-Data_in_Motion-Secure_Shell.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="Security_Guide-Encryption-Data_in_Motion-Virtual_Private_Networks">3.5. Virtual Private Networks</h2></div></div></div><div class="para">
Virtual Private Networks (VPN) provide encrypted tunnels between computers or networks of computers across all ports. With a VPN in place, all network traffic from the client is forwarded to the server through the encrypted tunnel. This means that the client is logically on the same network as the server it is connected to via the VPN. VPNs are very common and are simple to use and setup.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="Security_Guide-Encryption-Data_in_Motion.html"><strong>Prev</strong>3.4. Data in Motion</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="Security_Guide-Encryption-Data_in_Motion-Secure_Shell.html"><strong>Next</strong>3.6. Secure Shell</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>3.4. Data in Motion</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="chap-Security_Guide-Encryption.html" title="Chapter 3. Encryption"/><link rel="prev" href="Security_Guide-Encryption-Protecting_Data_at_Rest-File_Based_Encryption.html" title="3.3. File Based Encryption"/><link rel="next" href="Security_Guide-Encryption-Data_in_Motion-Virtual_Private_Networks.html" title="3.5. Virtual Private Networks"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/
></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="Security_Guide-Encryption-Protecting_Data_at_Rest-File_Based_Encryption.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="Security_Guide-Encryption-Data_in_Motion-Virtual_Private_Networks.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="Security_Guide-Encryption-Data_in_Motion">3.4. Data in Motion</h2></div></div></div><div class="para">
Data in motion is data that is being transmitted over a network. The biggest threats to data in motion are interception and alteration. Your user name and password should never be transmitted over a network without protection as it could be intercepted and used by someone else to impersonate you or gain access to sensitive information. Other private information such as bank account information should also be protected when transmitted across a network. If the network session was encrypted then you would not have to worry as much about the data being compromised while it is being transmitted.
</div><div class="para">
Data in motion is particularly vulnerable to attackers because the attacker does not have to be near the computer in which the data is being stored rather they only have to be somewhere along the path. Encryption tunnels can protect data along the path of communications.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="Security_Guide-Encryption-Protecting_Data_at_Rest-File_Based_Encryption.html"><strong>Prev</strong>3.3. File Based Encryption</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="Security_Guide-Encryption-Data_in_Motion-Virtual_Private_Networks.html"><strong>Next</strong>3.5. Virtual Private Networks</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>3.3. File Based Encryption</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="chap-Security_Guide-Encryption.html" title="Chapter 3. Encryption"/><link rel="prev" href="sect-Security_Guide-Encryption-Protecting_Data_at_Rest-Full_Disk_Encryption.html" title="3.2. Full Disk Encryption"/><link rel="next" href="Security_Guide-Encryption-Data_in_Motion.html" title="3.4. Data in Motion"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docna
v"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Encryption-Protecting_Data_at_Rest-Full_Disk_Encryption.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="Security_Guide-Encryption-Data_in_Motion.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="Security_Guide-Encryption-Protecting_Data_at_Rest-File_Based_Encryption">3.3. File Based Encryption</h2></div></div></div><div class="para">
GnuPG (GPG) is an open source version of PGP that allows you to sign and/or encrypt a file or an email message. This is useful to maintain integrity of the message or file and also protects the confidentiality of the information contained within the file or email. In the case of email, GPG provides dual protection. Not only can it provide Data at Rest protection but also Data In Motion protection once the message has been sent across the network.
</div><div class="para">
File based encryption is intended to protect a file after it has left your computer, such as when you send a CD through the mail. Some file based encryption solutions will leave remnants of the encrypted files that an attacker who has physical access to your computer can recover under some circumstances. To protect the contents of those files from attackers who may have access to your computer, use file based encryption combined with another solution such as full disk encryption.
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2. We Need Feedback!</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="pref-Security_Guide-Preface.html" title="Preface"/><link rel="prev" href="pref-Security_Guide-Preface.html" title="Preface"/><link rel="next" href="chap-Security_Guide-Security_Overview.html" title="Chapter 1. Security Overview"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="pref-Security_Guide-Preface.html"><str
ong>Prev</strong></a></li><li class="next"><a accesskey="n" href="chap-Security_Guide-Security_Overview.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="We_Need_Feedback">2. We Need Feedback!</h2></div></div></div><a id="d0e359" class="indexterm"/><div class="para">
More information about the Linux Security Guide project can be found at <a href="https://fedorahosted.org/securityguide">https://fedorahosted.org/securityguide</a>
</div><div class="para">
To provide feedback for the Security Guide, please file a bug in <a href="https://bugzilla.redhat.com/">https://bugzilla.redhat.com/</a>.
</div><div class="itemizedlist"><ul><li><div class="para">
Product = <span class="emphasis"><em>Fedora Hosted Projects</em></span>
</div></li><li><div class="para">
Component = <span class="emphasis"><em>Security_Guide</em></span>
</div></li></ul></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="pref-Security_Guide-Preface.html"><strong>Prev</strong>Preface</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="chap-Security_Guide-Security_Overview.html"><strong>Next</strong>Chapter 1. Security Overview</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Chapter 3. Encryption</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="index.html" title="Linux Security Guide"/><link rel="prev" href="sect-Security_Guide-Additional_Resources-Useful_IP_Tables_Websites.html" title="2.9.7.2. Useful IP Tables Websites"/><link rel="next" href="sect-Security_Guide-Encryption-Protecting_Data_at_Rest-Full_Disk_Encryption.html" title="3.2. Full Disk Encryption"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul cla
ss="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Additional_Resources-Useful_IP_Tables_Websites.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Encryption-Protecting_Data_at_Rest-Full_Disk_Encryption.html"><strong>Next</strong></a></li></ul><div class="chapter" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="chap-Security_Guide-Encryption">Chapter 3. Encryption</h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="chap-Security_Guide-Encryption.html#sect-Security_Guide-Encryption-Data_at_Rest">3.1. Data at Rest</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Encryption-Protecting_Data_at_Rest-Full_Disk_Encryption.html">3.2. Full Disk Encryption</a></span></dt><dt><span class="section"><a href="Security_Guide-Encryption-Protecting_Data_at_Rest-File_Based_Encryption.html">3.3. File Based Encryption</a></span></dt><dt><span class="sectio
n"><a href="Security_Guide-Encryption-Data_in_Motion.html">3.4. Data in Motion</a></span></dt><dt><span class="section"><a href="Security_Guide-Encryption-Data_in_Motion-Virtual_Private_Networks.html">3.5. Virtual Private Networks</a></span></dt><dt><span class="section"><a href="Security_Guide-Encryption-Data_in_Motion-Secure_Shell.html">3.6. Secure Shell</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-LUKS_Disk_Encryption.html">3.7. LUKS Disk Encryption</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-LUKS_Disk_Encryption.html#sect-Security_Guide-LUKS_Disk_Encryption-LUKS_Implementation_in_Fedora">3.7.1. LUKS Implementation in Fedora</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories.html">3.7.2. Manually Encrypting Directories</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-Ste
p_by_Step_Instructions.html">3.7.3. Step-by-Step Instructions</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-What_you_have_just_accomplished.html">3.7.4. What you have just accomplished.</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-LUKS_Disk_Encryption-Links_of_Interest.html">3.7.5. Links of Interest</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives.html">3.8. 7-Zip Encrypted Archives</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives.html#sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Installation">3.8.1. 7-Zip Installation in Fedora</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Installation-Instructions.html">3.8.2. Step-by-Step Installation Instructions</a></span></dt><dt><span
class="section"><a href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Usage_Instructions.html">3.8.3. Step-by-Step Usage Instructions</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Things_of_note.html">3.8.4. Things of note</a></span></dt></dl></dd></dl></div><div class="para">
There are two main types of data that must be protected: data at rest and data in motion. These different types of data are protected in similar ways using similar technology but the implementations can be completely different. No single protective implementation can prevent all possible methods of compromise as the same information may be at rest and in motion at different points in time.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-Encryption-Data_at_Rest">3.1. Data at Rest</h2></div></div></div><div class="para">
Data at rest is data that is stored on a hard drive, tape, CD, DVD, disk, or other media. This information's biggest threat comes from being physically stolen. Laptops in airports, CDs going through the mail, and backup tapes that get left in the wrong places are all examples of events where data can be compromised through theft. If the data was encrypted on the media then you wouldn't have to worry as much about the data being compromised.
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Chapter 4. General Principles of Information Security</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="index.html" title="Linux Security Guide"/><link rel="prev" href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Things_of_note.html" title="3.8.4. Things of note"/><link rel="next" href="sect-Security_Guide-General_Principles_of_Information_Security-Tips_Guides_and_Tools.html" title="4.2. Tips, Guides, and Tools"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="D
ocumentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Things_of_note.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-General_Principles_of_Information_Security-Tips_Guides_and_Tools.html"><strong>Next</strong></a></li></ul><div class="chapter" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="chap-Security_Guide-General_Principles_of_Information_Security">Chapter 4. General Principles of Information Security</h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="chap-Security_Guide-General_Principles_of_Information_Security.html#sect-Security_Guide-General_Principles_of_Information_Security-General_Principles">4.1. General Principles</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-General_Principles_of_Information_Security-Tips_Guides_and_Tools.html">4.2. Tips, Guides, and
Tools</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-General_Principles_of_Information_Security-NSA_Documents.html">4.3. NSA Documents</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-General_Principles_of_Information_Security-DISA_IASE_Documents.html">4.4. DISA IASE Documents</a></span></dt></dl></div><div class="para">
The United States' <a href="www.nsa.gov">National Security Agency</a> (NSA) provides hardening guides and hardening tips for many different operating systems to help government agencies, businesses, and individuals help secure their system against attacks. In addition to specific settings to change, a set of general principles have been developed to give you a high level view of information security.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-General_Principles_of_Information_Security-General_Principles">4.1. General Principles</h2></div></div></div><div class="itemizedlist"><ul><li><div class="para">
Encrypt all data transmitted over the network. Encrypting authentication information (such as passwords) is particularly important.
</div></li><li><div class="para">
Minimize the amount of software installed and running in order to minimize vulnerability.
</div></li><li><div class="para">
Use security-enhancing software and tools whenever available (e.g. SELinux and IPTables).
</div></li><li><div class="para">
Run each network service on a separate server whenever possible. This minimizes the risk that a compromise of one service could lead to a compromise of others.
</div></li><li><div class="para">
Maintain user accounts. Create a good password policy and enforce its use. Delete unused user accounts.
</div></li><li><div class="para">
Review system and application logs on a routine basis. Send logs to a dedicated log server. This prevents intruders from easily avoiding detection by modifying the local logs.
</div></li><li><div class="para">
Never login directly as root, unless absolutely necessary. Administrators should use sudo to execute commands as root when required. The accounts capable of using sudo are specified in /etc/sudoers, which is edited with the visudo utility. By default, relavent logs are written to /var/log/secure.
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Chapter 7. References</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="index.html" title="Linux Security Guide"/><link rel="prev" href="sect-Security_Guide-Software_Maintenance-Install_Signed_Packages_from_Well_Known_Repositories.html" title="6.4. Install Signed Packages from Well Known Repositories"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Software_Mainte
nance-Install_Signed_Packages_from_Well_Known_Repositories.html"><strong>Prev</strong></a></li><li class="next"/></ul><div class="chapter" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="chap-Security_Guide-References">Chapter 7. References</h2></div></div></div><a id="d0e16800" class="indexterm"/><a id="d0e16803" class="indexterm"/><a id="d0e16808" class="indexterm"/><a id="d0e16813" class="indexterm"/><a id="d0e16818" class="indexterm"/><a id="d0e16823" class="indexterm"/><a id="d0e16828" class="indexterm"/><a id="d0e16833" class="indexterm"/><a id="d0e16840" class="indexterm"/><a id="d0e16847" class="indexterm"/><a id="d0e16854" class="indexterm"/><div class="para">
The following references are pointers to additional information that is relevant to SELinux and Fedora but beyond the scope of this guide. Note that due to the rapid development of SELinux, some of this material may only apply to specific releases of Fedora.
</div><div class="variablelist" id="vari-Security_Guide-References-Books"><h6>Books</h6><dl><dt><span class="term">SELinux by Example</span></dt><dd><div class="para">
Mayer, MacMillan, and Caplan
</div><div class="para">
Prentice Hall, 2007
</div></dd></dl></div><div class="variablelist" id="vari-Security_Guide-References-Tutorials_and_Help"><h6>Tutorials and Help</h6><dl><dt><span class="term">Understanding and Customizing the Apache HTTP SELinux Policy</span></dt><dd><div class="para">
<a href="http://fedora.redhat.com/docs/selinux-apache-fc3/">http://fedora.redhat.com/docs/selinux-apache-fc3/</a>
</div></dd><dt><span class="term">Tutorials and talks from Russell Coker</span></dt><dd><div class="para">
<a href="http://www.coker.com.au/selinux/talks/ibmtu-2004/">http://www.coker.com.au/selinux/talks/ibmtu-2004/</a>
</div></dd><dt><span class="term">Generic Writing SELinux policy HOWTO</span></dt><dd><div class="para">
<a href="https://sourceforge.net/docman/display_doc.php?docid=21959[amp ]group_id=21266">https://sourceforge.net/docman/display_doc.php?docid=21959[amp ]group_id=21266</a>
</div></dd><dt><span class="term">Red Hat Knowledgebase</span></dt><dd><div class="para">
<a href="http://kbase.redhat.com/">http://kbase.redhat.com/</a>
</div></dd></dl></div><div class="variablelist" id="vari-Security_Guide-References-General_Information"><h6>General Information</h6><dl><dt><span class="term">NSA SELinux main website</span></dt><dd><div class="para">
<a href="http://www.nsa.gov/selinux/">http://www.nsa.gov/selinux/</a>
</div></dd><dt><span class="term">NSA SELinux FAQ</span></dt><dd><div class="para">
<a href="http://www.nsa.gov/selinux/info/faq.cfm">http://www.nsa.gov/selinux/info/faq.cfm</a>
</div></dd><dt><span class="term">Fedora SELinux FAQ </span></dt><dd><div class="para">
<a href="http://fedora.redhat.com/docs/selinux-faq-fc3/">http://fedora.redhat.com/docs/selinux-faq-fc3/</a>
</div></dd><dt><span class="term">SELinux NSA's Open Source Security Enhanced Linux</span></dt><dd><div class="para">
<a href="http://www.oreilly.com/catalog/selinux/">http://www.oreilly.com/catalog/selinux/</a>
</div></dd></dl></div><div class="variablelist" id="vari-Security_Guide-References-Technology"><h6>Technology</h6><dl><dt><span class="term">An Overview of Object Classes and Permissions</span></dt><dd><div class="para">
<a href="http://www.tresys.com/selinux/obj_perms_help.html">http://www.tresys.com/selinux/obj_perms_help.html</a>
</div></dd><dt><span class="term">Integrating Flexible Support for Security Policies into the Linux Operating System (a history of Flask implementation in Linux)</span></dt><dd><div class="para">
<a href="http://www.nsa.gov/selinux/papers/slinux-abs.cfm">http://www.nsa.gov/selinux/papers/slinux-abs.cfm</a>
</div></dd><dt><span class="term">Implementing SELinux as a Linux Security Module</span></dt><dd><div class="para">
<a href="http://www.nsa.gov/selinux/papers/module-abs.cfm">http://www.nsa.gov/selinux/papers/module-abs.cfm</a>
</div></dd><dt><span class="term">A Security Policy Configuration for the Security-Enhanced Linux</span></dt><dd><div class="para">
<a href="http://www.nsa.gov/selinux/papers/policy-abs.cfm">http://www.nsa.gov/selinux/papers/policy-abs.cfm</a>
</div></dd></dl></div><div class="variablelist" id="vari-Security_Guide-References-Community"><h6>Community</h6><dl><dt><span class="term">SELinux community page</span></dt><dd><div class="para">
<a href="http://selinux.sourceforge.net">http://selinux.sourceforge.net</a>
</div></dd><dt><span class="term">IRC</span></dt><dd><div class="para">
irc.freenode.net, #rhel-selinux
</div></dd></dl></div><div class="variablelist" id="vari-Security_Guide-References-History"><h6>History</h6><dl><dt><span class="term">Quick history of Flask</span></dt><dd><div class="para">
<a href="http://www.cs.utah.edu/flux/fluke/html/flask.html">http://www.cs.utah.edu/flux/fluke/html/flask.html</a>
</div></dd><dt><span class="term">Full background on Fluke</span></dt><dd><div class="para">
<a href="http://www.cs.utah.edu/flux/fluke/html/index.html">http://www.cs.utah.edu/flux/fluke/html/index.html</a>
</div></dd></dl></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Software_Maintenance-Install_Signed_Packages_from_Well_Known_Repositories.html"><strong>Prev</strong>6.4. Install Signed Packages from Well Known Repo...</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Chapter 5. Secure Installation</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="index.html" title="Linux Security Guide"/><link rel="prev" href="sect-Security_Guide-General_Principles_of_Information_Security-DISA_IASE_Documents.html" title="4.4. DISA IASE Documents"/><link rel="next" href="sect-Security_Guide-Secure_Installation-Utilize_LUKS_Partition_Encryption.html" title="5.2. Utilize LUKS Partition Encryption"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentat
ion Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-General_Principles_of_Information_Security-DISA_IASE_Documents.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Secure_Installation-Utilize_LUKS_Partition_Encryption.html"><strong>Next</strong></a></li></ul><div class="chapter" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="chap-Security_Guide-Secure_Installation">Chapter 5. Secure Installation</h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="chap-Security_Guide-Secure_Installation.html#sect-Security_Guide-Secure_Installation-Disk_Partitions">5.1. Disk Partitions</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Secure_Installation-Utilize_LUKS_Partition_Encryption.html">5.2. Utilize LUKS Partition Encryption</a></span></dt></dl></div><div class="para">
Security begins with the first time you put that CD or DVD into your disk drive to install Fedora. Configuring your system securely from the beginning makes it easier to implement additional security settings later.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-Secure_Installation-Disk_Partitions">5.1. Disk Partitions</h2></div></div></div><div class="para">
The NSA recommends creating separate partitions for /boot, /, /home, /tmp, and /var/tmp. The reasons for each are different and we will address each partition.
</div><div class="para">
/boot - This partition is the first partition that is read by the system during boot up. The boot loader and kernel images that are used to boot your system into Fedora are stored in this partition. This partition should not be encrypted. If this partition is included in / and that partition is encrypted or otherwise becomes unavailable then your system will not be able to boot.
</div><div class="para">
/home - When user data (/home) is stored in / instead of in a separate partition, the partition can fill up causing the operating system to become unstable. Also, when upgrading your system to the next version of Fedora it is a lot easier when you can keep your data in the /home partition as it will not be overwritten during installation. If the root partition (/) becomes corrupt your data could be lost forever. By using a separate partition there is slightly more protection against data loss. You can also target this partition for frequent backups.
</div><div class="para">
/tmp and /var/tmp - Both the /tmp and the /var/tmp directories are used to store data that doesn't need to be stored for a long period of time. However if a lot of data floods one of these directories it can consume all of your storage space. If this happens and these directories are stored within / then your system could become unstable and crash. For this reason, moving these directories into their own partitions is a good idea.
</div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-General_Principles_of_Information_Security-DISA_IASE_Documents.html"><strong>Prev</strong>4.4. DISA IASE Documents</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Secure_Installation-Utilize_LUKS_Partition_Encryption.html"><strong>Next</strong>5.2. Utilize LUKS Partition Encryption</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Chapter 2. Securing Your Network</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="index.html" title="Linux Security Guide"/><link rel="prev" href="sect-Security_Guide-Security_Updates.html" title="1.5. Security Updates"/><link rel="next" href="sect-Security_Guide-Server_Security.html" title="2.2. Server Security"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-S
ecurity_Updates.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Server_Security.html"><strong>Next</strong></a></li></ul><div class="chapter" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="chap-Security_Guide-Securing_Your_Network">Chapter 2. Securing Your Network</h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security">2.1. Workstation Security</a></span></dt><dd><dl><dt><span class="section"><a href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security-Evaluating_Workstation_Security">2.1.1. Evaluating Workstation Security</a></span></dt><dt><span class="section"><a href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security-BIOS_and_Boot_Loader_Security">2.1.2. BIOS and Boot Loader Security</a></span></dt><dt><span class="sect
ion"><a href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security-Password_Security">2.1.3. Password Security</a></span></dt><dt><span class="section"><a href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security-Administrative_Controls">2.1.4. Administrative Controls</a></span></dt><dt><span class="section"><a href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security-Available_Network_Services">2.1.5. Available Network Services</a></span></dt><dt><span class="section"><a href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security-Personal_Firewalls">2.1.6. Personal Firewalls</a></span></dt><dt><span class="section"><a href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security-Security_Enhanced_Communication_Tools">2.1.7. Security Enhanced Communication Tools</a></span></dt></dl></dd><dt><span class="s
ection"><a href="sect-Security_Guide-Server_Security.html">2.2. Server Security</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Server_Security.html#sect-Security_Guide-Server_Security-Securing_Services_With_TCP_Wrappers_and_xinetd">2.2.1. Securing Services With TCP Wrappers and xinetd</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Server_Security-Securing_Portmap.html">2.2.2. Securing Portmap</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Server_Security-Securing_NIS.html">2.2.3. Securing NIS</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Server_Security-Securing_NFS.html">2.2.4. Securing NFS</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Server_Security-Securing_the_Apache_HTTP_Server.html">2.2.5. Securing the Apache HTTP Server</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Server_Security-Securing_FTP.html">2.2.6. Securing FTP</
a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Server_Security-Securing_Sendmail.html">2.2.7. Securing Sendmail</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Server_Security-Verifying_Which_Ports_Are_Listening.html">2.2.8. Verifying Which Ports Are Listening</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Single_Sign_on_SSO.html">2.3. Single Sign-on (SSO)</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Single_Sign_on_SSO.html#sect-Security_Guide-Single_Sign_on_SSO-Introduction">2.3.1. Introduction</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Single_Sign_on_SSO-Getting_Started_with_your_new_Smart_Card.html">2.3.2. Getting Started with your new Smart Card</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Single_Sign_on_SSO-How_Smart_Card_Enrollment_Works.html">2.3.3. How Smart Card Enrollment Works</a></span></dt><dt><span cla
ss="section"><a href="sect-Security_Guide-Single_Sign_on_SSO-How_Smart_Card_Login_Works.html">2.3.4. How Smart Card Login Works</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Single_Sign_on_SSO-Configuring_Firefox_to_use_Kerberos_for_SSO.html">2.3.5. Configuring Firefox to use Kerberos for SSO</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM.html">2.4. Pluggable Authentication Modules (PAM)</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM.html#sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Advantages_of_PAM">2.4.1. Advantages of PAM</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_Configuration_Files.html">2.4.2. PAM Configuration Files</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_Conf
iguration_File_Format.html">2.4.3. PAM Configuration File Format</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Sample_PAM_Configuration_Files.html">2.4.4. Sample PAM Configuration Files</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Creating_PAM_Modules.html">2.4.5. Creating PAM Modules</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Administrative_Credential_Caching.html">2.4.6. PAM and Administrative Credential Caching</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Device_Ownership.html">2.4.7. PAM and Device Ownership</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Additional_Resources.html">2.4.8. Additional Resources</a></span></dt></dl></dd><dt><span class="se
ction"><a href="sect-Security_Guide-TCP_Wrappers_and_xinetd.html">2.5. TCP Wrappers and xinetd</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-TCP_Wrappers_and_xinetd.html#sect-Security_Guide-TCP_Wrappers_and_xinetd-TCP_Wrappers">2.5.1. TCP Wrappers</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-TCP_Wrappers_and_xinetd-TCP_Wrappers_Configuration_Files.html">2.5.2. TCP Wrappers Configuration Files</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-TCP_Wrappers_and_xinetd-xinetd.html">2.5.3. xinetd</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-TCP_Wrappers_and_xinetd-xinetd_Configuration_Files.html">2.5.4. xinetd Configuration Files</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-TCP_Wrappers_and_xinetd-Additional_Resources.html">2.5.5. Additional Resources</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Kerberos.html">2.6. Kerbe
ros</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Kerberos.html#sect-Security_Guide-Kerberos-What_is_Kerberos">2.6.1. What is Kerberos?</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-Kerberos_Terminology.html">2.6.2. Kerberos Terminology</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-How_Kerberos_Works.html">2.6.3. How Kerberos Works</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-Kerberos_and_PAM.html">2.6.4. Kerberos and PAM</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Server.html">2.6.5. Configuring a Kerberos 5 Server</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Client.html">2.6.6. Configuring a Kerberos 5 Client</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-Domain_to_Realm_Mapping.html">2.6.7. Dom
ain-to-Realm Mapping</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-Setting_Up_Secondary_KDCs.html">2.6.8. Setting Up Secondary KDCs</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-Setting_Up_Cross_Realm_Authentication.html">2.6.9. Setting Up Cross Realm Authentication</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-Additional_Resources.html">2.6.10. Additional Resources</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPNs.html">2.7. Virtual Private Networks (VPNs)</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPNs.html#sect-Security_Guide-Virtual_Private_Networks_VPNs-How_Does_a_VPN_Work">2.7.1. How Does a VPN Work?</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPNs-VPNs_and_PROD.html">2.7.2. VPNs and Fedora</a></span></d
t><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec.html">2.7.3. IPsec</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPNs-Creating_an_IPsec_Connection.html">2.7.4. Creating an IPsec Connection</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec_Installation.html">2.7.5. IPsec Installation</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec_Host_to_Host_Configuration.html">2.7.6. IPsec Host-to-Host Configuration</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec_Network_to_Network_Configuration.html">2.7.7. IPsec Network-to-Network Configuration</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPNs-Starting_and_Stopping_an_IPsec_Connection.html">2.7.8. Starting and Stopping an IPsec
Connection</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Firewalls.html">2.8. Firewalls</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Firewalls.html#sect-Security_Guide-Firewalls-Netfilter_and_IPTables">2.8.1. Netfilter and IPTables</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Firewalls-Basic_Firewall_Configuration.html">2.8.2. Basic Firewall Configuration</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Firewalls-Using_IPTables.html">2.8.3. Using IPTables</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Firewalls-Common_IPTables_Filtering.html">2.8.4. Common IPTables Filtering</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Firewalls-FORWARD_and_NAT_Rules.html">2.8.5. FORWARD and NAT Rules</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Firewalls-Malicious_Software_and_Spoofed_IP_Addresses.html">2.8
.6. Malicious Software and Spoofed IP Addresses</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Firewalls-IPTables_and_Connection_Tracking.html">2.8.7. IPTables and Connection Tracking</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Firewalls-IPv6.html">2.8.8. IPv6</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Firewalls-Additional_Resources.html">2.8.9. Additional Resources</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-IPTables.html">2.9. IPTables</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-IPTables.html#sect-Security_Guide-IPTables-Packet_Filtering">2.9.1. Packet Filtering</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-IPTables-Differences_Between_IPTables_and_IPChains.html">2.9.2. Differences Between IPTables and IPChains</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-IPTables-Command_Options_f
or_IPTables.html">2.9.3. Command Options for IPTables</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-IPTables-Saving_IPTables_Rules.html">2.9.4. Saving IPTables Rules</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-IPTables-IPTables_Control_Scripts.html">2.9.5. IPTables Control Scripts</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-IPTables-IPTables_and_IPv6.html">2.9.6. IPTables and IPv6</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-IPTables-Additional_Resources.html">2.9.7. Additional Resources</a></span></dt></dl></dd></dl></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-Workstation_Security">2.1. Workstation Security</h2></div></div></div><a id="d0e1757" class="indexterm"/><div class="para">
Securing a Linux environment begins with the workstation. Whether locking down a personal machine or securing an enterprise system, sound security policy begins with the individual computer. A computer network is only as secure as its weakest node.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Workstation_Security-Evaluating_Workstation_Security">2.1.1. Evaluating Workstation Security</h3></div></div></div><a id="d0e1765" class="indexterm"/><a id="d0e1772" class="indexterm"/><a id="d0e1779" class="indexterm"/><a id="d0e1786" class="indexterm"/><a id="d0e1793" class="indexterm"/><a id="d0e1800" class="indexterm"/><div class="para">
When evaluating the security of a Fedora workstation, consider the following:
</div><div class="itemizedlist"><ul><li><div class="para">
<span class="emphasis"><em>BIOS and Boot Loader Security</em></span> — Can an unauthorized user physically access the machine and boot into single user or rescue mode without a password?
</div></li><li><div class="para">
<span class="emphasis"><em>Password Security</em></span> — How secure are the user account passwords on the machine?
</div></li><li><div class="para">
<span class="emphasis"><em>Administrative Controls</em></span> — Who has an account on the system and how much administrative control do they have?
</div></li><li><div class="para">
<span class="emphasis"><em>Available Network Services</em></span> — What services are listening for requests from the network and should they be running at all?
</div></li><li><div class="para">
<span class="emphasis"><em>Personal Firewalls</em></span> — What type of firewall, if any, is necessary?
</div></li><li><div class="para">
<span class="emphasis"><em>Security Enhanced Communication Tools</em></span> — Which tools should be used to communicate between workstations and which should be avoided?
</div></li></ul></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Workstation_Security-BIOS_and_Boot_Loader_Security">2.1.2. BIOS and Boot Loader Security</h3></div></div></div><a id="d0e1849" class="indexterm"/><a id="d0e1854" class="indexterm"/><a id="d0e1859" class="indexterm"/><div class="para">
Password protection for the BIOS (or BIOS equivalent) and the boot loader can prevent unauthorized users who have physical access to systems from booting using removable media or obtaining root privileges through single user mode. The security measures you should take to protect against such attacks depends both on the sensitivity of the information on the workstation and the location of the machine.
</div><div class="para">
For example, if a machine is used in a trade show and contains no sensitive information, then it may not be critical to prevent such attacks. However, if an employee's laptop with private, unencrypted SSH keys for the corporate network is left unattended at that same trade show, it could lead to a major security breach with ramifications for the entire company.
</div><div class="para">
If the workstation is located in a place where only authorized or trusted people have access, however, then securing the BIOS or the boot loader may not be necessary.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-BIOS_and_Boot_Loader_Security-BIOS_Passwords">2.1.2.1. BIOS Passwords</h4></div></div></div><a id="d0e1873" class="indexterm"/><div class="para">
The two primary reasons for password protecting the BIOS of a computer are<sup>[<a id="d0e1882" href="#ftn.d0e1882" class="footnote">5</a>]</sup>:
</div><div class="orderedlist"><ol><li><div class="para">
<span class="emphasis"><em>Preventing Changes to BIOS Settings</em></span> — If an intruder has access to the BIOS, they can set it to boot from a diskette or CD-ROM. This makes it possible for them to enter rescue mode or single user mode, which in turn allows them to start arbitrary processes on the system or copy sensitive data.
</div></li><li><div class="para">
<span class="emphasis"><em>Preventing System Booting</em></span> — Some BIOSes allow password protection of the boot process. When activated, an attacker is forced to enter a password before the BIOS launches the boot loader.
</div></li></ol></div><div class="para">
Because the methods for setting a BIOS password vary between computer manufacturers, consult the computer's manual for specific instructions.
</div><div class="para">
If you forget the BIOS password, it can either be reset with jumpers on the motherboard or by disconnecting the CMOS battery. For this reason, it is good practice to lock the computer case if possible. However, consult the manual for the computer or motherboard before attempting to disconnect the CMOS battery.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-BIOS_Passwords-Securing_Non_x86_Platforms">2.1.2.1.1. Securing Non-x86 Platforms</h5></div></div></div><a id="d0e1906" class="indexterm"/><a id="d0e1913" class="indexterm"/><div class="para">
Other architectures use different programs to perform low-level tasks roughly equivalent to those of the BIOS on x86 systems. For instance, <span class="trademark">Intel</span>® <span class="trademark">Itanium</span>™ computers use the <em class="firstterm">Extensible Firmware Interface</em> (<em class="firstterm">EFI</em>) shell.
</div><div class="para">
For instructions on password protecting BIOS-like programs on other architectures, refer to the manufacturer's instructions.
</div></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-BIOS_and_Boot_Loader_Security-Boot_Loader_Passwords">2.1.2.2. Boot Loader Passwords</h4></div></div></div><a id="d0e1939" class="indexterm"/><a id="d0e1944" class="indexterm"/><div class="para">
The primary reasons for password protecting a Linux boot loader are as follows:
</div><div class="orderedlist"><ol><li><div class="para">
<span class="emphasis"><em>Preventing Access to Single User Mode</em></span> — If attackers can boot the system into single user mode, they are logged in automatically as root without being prompted for the root password.
</div></li><li><div class="para">
<span class="emphasis"><em>Preventing Access to the GRUB Console</em></span> — If the machine uses GRUB as its boot loader, an attacker can use the GRUB editor interface to change its configuration or to gather information using the <code class="command">cat</code> command.
</div></li><li><div class="para">
<span class="emphasis"><em>Preventing Access to Insecure Operating Systems</em></span> — If it is a dual-boot system, an attacker can select an operating system at boot time (for example, DOS), which ignores access controls and file permissions.
</div></li></ol></div><div class="para">
Fedora ships with the GRUB boot loader on the x86 platform. For a detailed look at GRUB, refer to the Red Hat Installation Guide.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Boot_Loader_Passwords-Password_Protecting_GRUB">2.1.2.2.1. Password Protecting GRUB</h5></div></div></div><a id="d0e1980" class="indexterm"/><div class="para">
You can configure GRUB to address the first two issues listed in <a class="xref" href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-BIOS_and_Boot_Loader_Security-Boot_Loader_Passwords" title="2.1.2.2. Boot Loader Passwords">Section 2.1.2.2, “Boot Loader Passwords”</a> by adding a password directive to its configuration file. To do this, first choose a strong password, open a shell, log in as root, and then type the following command:
</div><pre class="screen"><code class="command">/sbin/grub-md5-crypt</code>
</pre><div class="para">
When prompted, type the GRUB password and press <span class="keycap"><strong>Enter</strong></span>. This returns an MD5 hash of the password.
</div><div class="para">
Next, edit the GRUB configuration file <code class="filename">/boot/grub/grub.conf</code>. Open the file and below the <code class="command">timeout</code> line in the main section of the document, add the following line:
</div><pre class="screen"><code class="command">password --md5 <em class="replaceable"><code><password-hash></code></em></code>
</pre><div class="para">
Replace <em class="replaceable"><code><password-hash></code></em> with the value returned by <code class="command">/sbin/grub-md5-crypt</code><sup>[<a id="d0e2021" href="#ftn.d0e2021" class="footnote">6</a>]</sup>.
</div><div class="para">
The next time the system boots, the GRUB menu prevents access to the editor or command interface without first pressing <span class="keycap"><strong>p</strong></span> followed by the GRUB password.
</div><div class="para">
Unfortunately, this solution does not prevent an attacker from booting into an insecure operating system in a dual-boot environment. For this, a different part of the <code class="filename">/boot/grub/grub.conf</code> file must be edited.
</div><div class="para">
Look for the <code class="computeroutput">title</code> line of the operating system that you want to secure, and add a line with the <code class="command">lock</code> directive immediately beneath it.
</div><div class="para">
For a DOS system, the stanza should begin similar to the following:
</div><pre class="screen"><code class="computeroutput">title DOS lock</code>
</pre><div class="warning"><h2>Warning</h2><div class="para">
A <code class="computeroutput">password</code> line must be present in the main section of the <code class="filename">/boot/grub/grub.conf</code> file for this method to work properly. Otherwise, an attacker can access the GRUB editor interface and remove the lock line.
</div></div><div class="para">
To create a different password for a particular kernel or operating system, add a <code class="command">lock</code> line to the stanza, followed by a password line.
</div><div class="para">
Each stanza protected with a unique password should begin with lines similar to the following example:
</div><pre class="screen"><code class="computeroutput">title DOS lock password --md5 <em class="replaceable"><code><password-hash></code></em></code>
</pre></div></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Workstation_Security-Password_Security">2.1.3. Password Security</h3></div></div></div><a id="d0e2076" class="indexterm"/><div class="para">
Passwords are the primary method that Fedora uses to verify a user's identity. This is why password security is so important for protection of the user, the workstation, and the network.
</div><div class="para">
For security purposes, the installation program configures the system to use <em class="firstterm">Message-Digest Algorithm</em> (<span class="emphasis"><em>MD5</em></span>) and shadow passwords. It is highly recommended that you do not alter these settings.
</div><div class="para">
If MD5 passwords are deselected during installation, the older <em class="firstterm">Data Encryption Standard</em> (<em class="firstterm"><acronym class="acronym">DES</acronym></em>) format is used. This format limits passwords to eight alphanumeric characters (disallowing punctuation and other special characters), and provides a modest 56-bit level of encryption.
</div><div class="para">
If shadow passwords are deselected during installation, all passwords are stored as a one-way hash in the world-readable <code class="filename">/etc/passwd</code> file, which makes the system vulnerable to offline password cracking attacks. If an intruder can gain access to the machine as a regular user, he can copy the <code class="filename">/etc/passwd</code> file to his own machine and run any number of password cracking programs against it. If there is an insecure password in the file, it is only a matter of time before the password cracker discovers it.
</div><div class="para">
Shadow passwords eliminate this type of attack by storing the password hashes in the file <code class="filename">/etc/shadow</code>, which is readable only by the root user.
</div><div class="para">
This forces a potential attacker to attempt password cracking remotely by logging into a network service on the machine, such as SSH or FTP. This sort of brute-force attack is much slower and leaves an obvious trail as hundreds of failed login attempts are written to system files. Of course, if the cracker starts an attack in the middle of the night on a system with weak passwords, the cracker may have gained access before dawn and edited the log files to cover his tracks.
</div><div class="para">
In addition to format and storage considerations is the issue of content. The single most important thing a user can do to protect his account against a password cracking attack is create a strong password.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Password_Security-Creating_Strong_Passwords">2.1.3.1. Creating Strong Passwords</h4></div></div></div><a id="d0e2118" class="indexterm"/><div class="para">
When creating a secure password, it is a good idea to follow these guidelines:
</div><div class="itemizedlist"><ul><li><div class="para">
<span class="emphasis"><em>Do Not Use Only Words or Numbers</em></span> — Never use only numbers or words in a password.
</div><div class="para">
Some insecure examples include the following:
</div><div class="itemizedlist"><ul><li><div class="para">
8675309
</div></li><li><div class="para">
juan
</div></li><li><div class="para">
hackme
</div></li></ul></div></li><li><div class="para">
<span class="emphasis"><em>Do Not Use Recognizable Words</em></span> — Words such as proper names, dictionary words, or even terms from television shows or novels should be avoided, even if they are bookended with numbers.
</div><div class="para">
Some insecure examples include the following:
</div><div class="itemizedlist"><ul><li><div class="para">
john1
</div></li><li><div class="para">
DS-9
</div></li><li><div class="para">
mentat123
</div></li></ul></div></li><li><div class="para">
<span class="emphasis"><em>Do Not Use Words in Foreign Languages</em></span> — Password cracking programs often check against word lists that encompass dictionaries of many languages. Relying on foreign languages for secure passwords is not secure.
</div><div class="para">
Some insecure examples include the following:
</div><div class="itemizedlist"><ul><li><div class="para">
cheguevara
</div></li><li><div class="para">
bienvenido1
</div></li><li><div class="para">
1dumbKopf
</div></li></ul></div></li><li><div class="para">
<span class="emphasis"><em>Do Not Use Hacker Terminology</em></span> — If you think you are elite because you use hacker terminology — also called l337 (LEET) speak — in your password, think again. Many word lists include LEET speak.
</div><div class="para">
Some insecure examples include the following:
</div><div class="itemizedlist"><ul><li><div class="para">
H4X0R
</div></li><li><div class="para">
1337
</div></li></ul></div></li><li><div class="para">
<span class="emphasis"><em>Do Not Use Personal Information</em></span> — Avoid using any personal information in your passwords. If the attacker knows your identity, the task of deducing your password becomes easier. The following is a list of the types of information to avoid when creating a password:
</div><div class="para">
Some insecure examples include the following:
</div><div class="itemizedlist"><ul><li><div class="para">
Your name
</div></li><li><div class="para">
The names of pets
</div></li><li><div class="para">
The names of family members
</div></li><li><div class="para">
Any birth dates
</div></li><li><div class="para">
Your phone number or zip code
</div></li></ul></div></li><li><div class="para">
<span class="emphasis"><em>Do Not Invert Recognizable Words</em></span> — Good password checkers always reverse common words, so inverting a bad password does not make it any more secure.
</div><div class="para">
Some insecure examples include the following:
</div><div class="itemizedlist"><ul><li><div class="para">
R0X4H
</div></li><li><div class="para">
nauj
</div></li><li><div class="para">
9-DS
</div></li></ul></div></li><li><div class="para">
<span class="emphasis"><em>Do Not Write Down Your Password</em></span> — Never store a password on paper. It is much safer to memorize it.
</div></li><li><div class="para">
<span class="emphasis"><em>Do Not Use the Same Password For All Machines</em></span> — It is important to make separate passwords for each machine. This way if one system is compromised, all of your machines are not immediately at risk.
</div></li></ul></div><div class="para">
The following guidelines will help you to create a strong password:
</div><div class="itemizedlist"><ul><li><div class="para">
<span class="emphasis"><em>Make the Password at Least Eight Characters Long</em></span> — The longer the password, the better. If using MD5 passwords, it should be 15 characters or longer. With DES passwords, use the maximum length (eight characters).
</div></li><li><div class="para">
<span class="emphasis"><em>Mix Upper and Lower Case Letters</em></span> — Fedora is case sensitive, so mix cases to enhance the strength of the password.
</div></li><li><div class="para">
<span class="emphasis"><em>Mix Letters and Numbers</em></span> — Adding numbers to passwords, especially when added to the middle (not just at the beginning or the end), can enhance password strength.
</div></li><li><div class="para">
<span class="emphasis"><em>Include Non-Alphanumeric Characters</em></span> — Special characters such as &, $, and > can greatly improve the strength of a password (this is not possible if using DES passwords).
</div></li><li><div class="para">
<span class="emphasis"><em>Pick a Password You Can Remember</em></span> — The best password in the world does little good if you cannot remember it; use acronyms or other mnemonic devices to aid in memorizing passwords.
</div></li></ul></div><div class="para">
With all these rules, it may seem difficult to create a password that meets all of the criteria for good passwords while avoiding the traits of a bad one. Fortunately, there are some steps you can take to generate an easily-remembered, secure password.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Creating_Strong_Passwords-Secure_Password_Creation_Methodology">2.1.3.1.1. Secure Password Creation Methodology</h5></div></div></div><a id="d0e2287" class="indexterm"/><div class="para">
There are many methods that people use to create secure passwords. One of the more popular methods involves acronyms. For example:
</div><div class="itemizedlist"><ul><li><div class="para">
Think of an easily-remembered phrase, such as:
</div><div class="para">
"over the river and through the woods, to grandmother's house we go."
</div></li><li><div class="para">
Next, turn it into an acronym (including the punctuation).
</div><div class="para">
<strong class="userinput"><code>otrattw,tghwg.</code></strong>
</div></li><li><div class="para">
Add complexity by substituting numbers and symbols for letters in the acronym. For example, substitute <strong class="userinput"><code>7</code></strong> for <strong class="userinput"><code>t</code></strong> and the at symbol (<strong class="userinput"><code>@</code></strong>) for <strong class="userinput"><code>a</code></strong>:
</div><div class="para">
<strong class="userinput"><code>o7r@77w,7ghwg.</code></strong>
</div></li><li><div class="para">
Add more complexity by capitalizing at least one letter, such as <strong class="userinput"><code>H</code></strong>.
</div><div class="para">
<strong class="userinput"><code>o7r@77w,7gHwg.</code></strong>
</div></li><li><div class="para">
<span class="emphasis"><em>Finally, do not use the example password above for any systems, ever</em></span>.
</div></li></ul></div><div class="para">
While creating secure passwords is imperative, managing them properly is also important, especially for system administrators within larger organizations. The following section details good practices for creating and managing user passwords within an organization.
</div></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Password_Security-Creating_User_Passwords_Within_an_Organization">2.1.3.2. Creating User Passwords Within an Organization</h4></div></div></div><a id="d0e2350" class="indexterm"/><a id="d0e2355" class="indexterm"/><div class="para">
If an organization has a large number of users, the system administrators have two basic options available to force the use of good passwords. They can create passwords for the user, or they can let users create their own passwords, while verifying the passwords are of acceptable quality.
</div><div class="para">
Creating the passwords for the users ensures that the passwords are good, but it becomes a daunting task as the organization grows. It also increases the risk of users writing their passwords down.
</div><div class="para">
For these reasons, most system administrators prefer to have the users create their own passwords, but actively verify that the passwords are good and, in some cases, force users to change their passwords periodically through password aging.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Creating_User_Passwords_Within_an_Organization-Forcing_Strong_Passwords">2.1.3.2.1. Forcing Strong Passwords</h5></div></div></div><a id="d0e2369" class="indexterm"/><a id="d0e2374" class="indexterm"/><a id="d0e2379" class="indexterm"/><div class="para">
To protect the network from intrusion it is a good idea for system administrators to verify that the passwords used within an organization are strong ones. When users are asked to create or change passwords, they can use the command line application <code class="command">passwd</code>, which is <em class="firstterm">Pluggable Authentication Manager</em> (<em class="firstterm">PAM</em>) aware and therefore checks to see if the password is too short or otherwise easy to crack. This check is performed using the <code class="filename">pam_cracklib.so</code> PAM module. Since PAM is customizable, it is possible to add more password integrity checkers, such as <code class="filename">pam_passwdqc</code> (available from <a href="http://www.openwall.com/passwdqc/">http://www.openwall.com/passwdqc/</a>) or to write a new module. For a list of available PAM modules, refer to <a href="http://www.kernel.org/pub/linux/libs/pam/modules.html">http://www.kernel.org/pub/linux/libs/pam/mod
ules.html</a>. For more information about PAM, refer to <a class="xref" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM.html" title="2.4. Pluggable Authentication Modules (PAM)">Section 2.4, “Pluggable Authentication Modules (PAM)”</a>.
</div><div class="para">
The password check that is performed at the time of their creation does not discover bad passwords as effectively as running a password cracking program against the passwords.
</div><div class="para">
Many password cracking programs are available that run under Fedora, although none ship with the operating system. Below is a brief list of some of the more popular password cracking programs:
</div><div class="note"><h2>Note</h2><div class="para">
None of these tools are supplied with Fedora and are therefore not supported by Fedora. in any way.
</div></div><a id="d0e2418" class="indexterm"/><a id="d0e2423" class="indexterm"/><a id="d0e2431" class="indexterm"/><a id="d0e2439" class="indexterm"/><div class="itemizedlist"><ul><li><div class="para">
<span class="emphasis"><em><span class="application"><strong>John The Ripper</strong></span></em></span> — A fast and flexible password cracking program. It allows the use of multiple word lists and is capable of brute-force password cracking. It is available online at <a href="http://www.openwall.com/john/">http://www.openwall.com/john/</a>.
</div></li><li><div class="para">
<span class="emphasis"><em><span class="application"><strong>Crack</strong></span></em></span> — Perhaps the most well known password cracking software, <span class="application"><strong>Crack</strong></span> is also very fast, though not as easy to use as <span class="application"><strong>John The Ripper</strong></span>. It can be found online at <a href="http://www.crypticide.com/users/alecm/">http://www.crypticide.com/users/alecm/</a>.
</div></li><li><div class="para">
<span class="emphasis"><em><span class="application"><strong>Slurpie</strong></span></em></span> — <span class="application"><strong>Slurpie</strong></span> is similar to <span class="application"><strong>John The Ripper</strong></span> and <span class="application"><strong>Crack</strong></span>, but it is designed to run on multiple computers simultaneously, creating a distributed password cracking attack. It can be found along with a number of other distributed attack security evaluation tools online at <a href="http://www.ussrback.com/distributed.htm">http://www.ussrback.com/distributed.htm</a>.
</div></li></ul></div><div class="warning"><h2>Warning</h2><div class="para">
Always get authorization in writing before attempting to crack passwords within an organization.
</div></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Creating_User_Passwords_Within_an_Organization-Password_Aging">2.1.3.2.2. Password Aging</h5></div></div></div><a id="d0e2501" class="indexterm"/><a id="d0e2506" class="indexterm"/><div class="para">
Password aging is another technique used by system administrators to defend against bad passwords within an organization. Password aging means that after a specified period (usually 90 days), the user is prompted to create a new password. The theory behind this is that if a user is forced to change his password periodically, a cracked password is only useful to an intruder for a limited amount of time. The downside to password aging, however, is that users are more likely to write their passwords down.
</div><div class="para">
There are two primary programs used to specify password aging under Fedora: the <code class="command">chage</code> command or the graphical <span class="application"><strong>User Manager</strong></span> (<code class="command">system-config-users</code>) application.
</div><div class="para">
The <code class="option">-M</code> option of the <code class="command">chage</code> command specifies the maximum number of days the password is valid. For example, to set a user's password to expire in 90 days, use the following command:
</div><pre class="screen"><code class="command">chage -M 90 <em class="replaceable"><code><username></code></em></code>
</pre><div class="para">
In the above command, replace <em class="replaceable"><code><username></code></em> with the name of the user. To disable password expiration, it is traditional to use a value of <code class="command">99999</code> after the <code class="option">-M</code> option (this equates to a little over 273 years).
</div><div class="para">
You can also use the <code class="command">chage</code> command in interactive mode to modify multiple password aging and account details. Use the following command to enter interactive mode:
</div><pre class="screen"><code class="command">chage <em class="replaceable"><code><username></code></em></code>
</pre><div class="para">
The following is a sample interactive session using this command:
</div><pre class="screen"><code class="computeroutput"> [root@interch-dev1 ~]# chage davido Changing the aging information for davido Enter the new value, or press ENTER for the default Minimum Password Age [0]: 10 Maximum Password Age [99999]: 90 Last Password Change (YYYY-MM-DD) [2006-08-18]: Password Expiration Warning [7]: Password Inactive [-1]: Account Expiration Date (YYYY-MM-DD) [1969-12-31]: [root@interch-dev1 ~]# </code>
</pre><div class="para">
Refer to the man page for chage for more information on the available options.
</div><div class="para">
You can also use the graphical <span class="application"><strong>User Manager</strong></span> application to create password aging policies, as follows. Note: you need Administrator privileges to perform this procedure.
</div><div class="procedure"><ol class="1"><li><div class="para">
Click the <span class="guimenu"><strong>System</strong></span> menu on the Panel, point to <span class="guisubmenu"><strong>Administration</strong></span> and then click <span class="guimenuitem"><strong>Users and Groups</strong></span> to display the User Manager. Alternatively, type the command <code class="command">system-config-users</code> at a shell prompt.
</div></li><li><div class="para">
Click the <span class="guilabel"><strong>Users</strong></span> tab, and select the required user in the list of users.
</div></li><li><div class="para">
Click <span class="guibutton"><strong>Properties</strong></span> on the toolbar to display the User Properties dialog box (or choose <span class="guimenuitem"><strong>Properties</strong></span> on the <span class="guimenu"><strong>File</strong></span> menu).
</div></li><li><div class="para">
Click the <span class="guilabel"><strong>Password Info</strong></span> tab, and select the check box for <span class="guilabel"><strong>Enable password expiration</strong></span>.
</div></li><li><div class="para">
Enter the required value in the <span class="guilabel"><strong>Days before change required</strong></span> field, and click <span class="guibutton"><strong>OK</strong></span>.
</div></li></ol></div><div class="figure" id="figu-Security_Guide-Password_Aging-Specifying_password_aging_options"><div class="figure-contents"><div class="mediaobject"><img src="images/user_pass_info.png" alt="Specifying password aging options"/><div class="longdesc"><div class="para">
<span class="guilabel"><strong>Password Info</strong></span> pane illustration.
</div></div></div></div><h6>Figure 2.1. Specifying password aging options</h6></div><br class="figure-break"/></div></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Workstation_Security-Administrative_Controls">2.1.4. Administrative Controls</h3></div></div></div><div class="para">
When administering a home machine, the user must perform some tasks as the root user or by acquiring effective root privileges via a <em class="firstterm">setuid</em> program, such as <code class="command">sudo</code> or <code class="command">su</code>. A setuid program is one that operates with the user ID (<span class="emphasis"><em>UID</em></span>) of the program's owner rather than the user operating the program. Such programs are denoted by an <code class="computeroutput">s</code> in the owner section of a long format listing, as in the following example:
</div><pre class="screen"><code class="computeroutput">-rwsr-xr-x 1 root root 47324 May 1 08:09 /bin/su</code>
</pre><div class="note"><h2>Note</h2><div class="para">
The <code class="computeroutput">s</code> may be upper case or lower case. If it appears as upper case, it means that the underlying permission bit has not been set.
</div></div><div class="para">
For the system administrators of an organization, however, choices must be made as to how much administrative access users within the organization should have to their machine. Through a PAM module called <code class="filename">pam_console.so</code>, some activities normally reserved only for the root user, such as rebooting and mounting removable media are allowed for the first user that logs in at the physical console (refer to <a class="xref" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM.html" title="2.4. Pluggable Authentication Modules (PAM)">Section 2.4, “Pluggable Authentication Modules (PAM)”</a> for more information about the <code class="filename">pam_console.so</code> module.) However, other important system administration tasks, such as altering network settings, configuring a new mouse, or mounting network devices, are not possible without administrative privileges. As a result, system administrators must decide how much access the users
on their network should receive.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Administrative_Controls-Allowing_Root_Access">2.1.4.1. Allowing Root Access</h4></div></div></div><a id="d0e2680" class="indexterm"/><a id="d0e2683" class="indexterm"/><a id="d0e2688" class="indexterm"/><div class="para">
If the users within an organization are trusted and computer-literate, then allowing them root access may not be an issue. Allowing root access by users means that minor activities, like adding devices or configuring network interfaces, can be handled by the individual users, leaving system administrators free to deal with network security and other important issues.
</div><div class="para">
On the other hand, giving root access to individual users can lead to the following issues:
</div><div class="itemizedlist"><ul><li><div class="para">
<span class="emphasis"><em>Machine Misconfiguration</em></span> — Users with root access can misconfigure their machines and require assistance to resolve issues. Even worse, they might open up security holes without knowing it.
</div></li><li><div class="para">
<span class="emphasis"><em>Running Insecure Services</em></span> — Users with root access might run insecure servers on their machine, such as FTP or Telnet, potentially putting usernames and passwords at risk. These services transmit this information over the network in plain text.
</div></li><li><div class="para">
<span class="emphasis"><em>Running Email Attachments As Root</em></span> — Although rare, email viruses that affect Linux do exist. The only time they are a threat, however, is when they are run by the root user.
</div></li></ul></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Administrative_Controls-Disallowing_Root_Access">2.1.4.2. Disallowing Root Access</h4></div></div></div><a id="d0e2719" class="indexterm"/><div class="para">
If an administrator is uncomfortable allowing users to log in as root for these or other reasons, the root password should be kept secret, and access to runlevel one or single user mode should be disallowed through boot loader password protection (refer to <a class="xref" href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-BIOS_and_Boot_Loader_Security-Boot_Loader_Passwords" title="2.1.2.2. Boot Loader Passwords">Section 2.1.2.2, “Boot Loader Passwords”</a> for more information on this topic.)
</div><div class="para">
<a class="xref" href="chap-Security_Guide-Securing_Your_Network.html#tabl-Security_Guide-Disallowing_Root_Access-Methods_of_Disabling_the_Root_Account" title="Table 2.1. Methods of Disabling the Root Account">Table 2.1, “Methods of Disabling the Root Account”</a> describes ways that an administrator can further ensure that root logins are disallowed:
</div><a id="d0e2732" class="indexterm"/><div class="table" id="tabl-Security_Guide-Disallowing_Root_Access-Methods_of_Disabling_the_Root_Account"><div class="table-contents"><table summary="Methods of Disabling the Root Account" border="1"><colgroup><col width="20*"/><col width="50*"/><col width="50*"/><col width="50*"/></colgroup><thead><tr><th>
Method
</th><th>
Description
</th><th>
Effects
</th><th>
Does Not Affect
</th></tr></thead><tbody><tr><td>
Changing the root shell.
</td><td>
Edit the <code class="filename">/etc/passwd</code> file and change the shell from <code class="command">/bin/bash</code> to <code class="command">/sbin/nologin</code>.
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> Prevents access to the root shell and logs any such attempts. </td></tr><tr><td> The following programs are prevented from accessing the root account: </td></tr><tr><td> · <code class="command">login</code></td></tr><tr><td> · <code class="command">gdm</code></td></tr><tr><td> · <code class="command">kdm</code></td></tr><tr><td> · <code class="command">xdm</code></td></tr><tr><td> · <code class="command">su</code></td></tr><tr><td> · <code class="command">ssh</code></td></tr><tr><td> · <code class="command">scp</code></td></tr><tr><td> · <code class="command">sftp</code></td></tr></table>
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> Programs that do not require a shell, such as FTP clients, mail clients, and many setuid programs. </td></tr><tr><td> The following programs are <span class="emphasis"><em>not</em></span> prevented from accessing the root account: </td></tr><tr><td> · <code class="command">sudo</code></td></tr><tr><td> · FTP clients </td></tr><tr><td> · Email clients </td></tr></table>
</td></tr><tr><td>
Disabling root access via any console device (tty).
</td><td>
An empty <code class="filename">/etc/securetty</code> file prevents root login on any devices attached to the computer.
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> Prevents access to the root account via the console or the network. The following programs are prevented from accessing the root account: </td></tr><tr><td> · <code class="command">login</code></td></tr><tr><td> · <code class="command">gdm</code></td></tr><tr><td> · <code class="command">kdm</code></td></tr><tr><td> · <code class="command">xdm</code></td></tr><tr><td> · Other network services that open a tty </td></tr></table>
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> Programs that do not log in as root, but perform administrative tasks through setuid or other mechanisms. </td></tr><tr><td> The following programs are <span class="emphasis"><em>not</em></span> prevented from accessing the root account: </td></tr><tr><td> · <code class="command">su</code></td></tr><tr><td> · <code class="command">sudo</code></td></tr><tr><td> · <code class="command">ssh</code></td></tr><tr><td> · <code class="command">scp</code></td></tr><tr><td> · <code class="command">sftp</code></td></tr></table>
</td></tr><tr><td>
Disabling root SSH logins.
</td><td>
Edit the <code class="filename">/etc/ssh/sshd_config</code> file and set the <code class="command">PermitRootLogin</code> parameter to <code class="command">no</code>.
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> Prevents root access via the OpenSSH suite of tools. The following programs are prevented from accessing the root account: </td></tr><tr><td> · <code class="command">ssh</code></td></tr><tr><td> · <code class="command">scp</code></td></tr><tr><td> · <code class="command">sftp</code></td></tr></table>
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> This only prevents root access to the OpenSSH suite of tools. </td></tr></table>
</td></tr><tr><td>
Use PAM to limit root access to services.
</td><td>
Edit the file for the target service in the <code class="filename">/etc/pam.d/</code> directory. Make sure the <code class="filename">pam_listfile.so</code> is required for authentication.<sup>[<a id="d0e2941" href="#ftn.d0e2941" class="footnote">a</a>]</sup>
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> Prevents root access to network services that are PAM aware. </td></tr><tr><td> The following services are prevented from accessing the root account: </td></tr><tr><td> · FTP clients </td></tr><tr><td> · Email clients </td></tr><tr><td> · <code class="command">login</code></td></tr><tr><td> · <code class="command">gdm</code></td></tr><tr><td> · <code class="command">kdm</code></td></tr><tr><td> · <code class="command">xdm</code></td></tr><tr><td> · <code class="command">ssh</code></td></tr><tr><td> · <code class="command">scp</code></td></tr><tr><td> · <code class="command">sftp</code></td></tr><tr><td> · Any PAM aware services </td></tr></table>
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> Programs and services that are not PAM aware. </td></tr></table>
</td></tr></tbody><tbody class="footnotes"><tr><td colspan="4"><div class="footnote"><p><sup>[<a id="ftn.d0e2941" href="#d0e2941" class="para">a</a>] </sup>
Refer to <a class="xref" href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Disallowing_Root_Access-Disabling_Root_Using_PAM" title="2.1.4.2.4. Disabling Root Using PAM">Section 2.1.4.2.4, “Disabling Root Using PAM”</a> for details.
</p></div></td></tr></tbody></table></div><h6>Table 2.1. Methods of Disabling the Root Account</h6></div><br class="table-break"/><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Disallowing_Root_Access-Disabling_the_Root_Shell">2.1.4.2.1. Disabling the Root Shell</h5></div></div></div><div class="para">
To prevent users from logging in directly as root, the system administrator can set the root account's shell to <code class="command">/sbin/nologin</code> in the <code class="filename">/etc/passwd</code> file. This prevents access to the root account through commands that require a shell, such as the <code class="command">su</code> and the <code class="command">ssh</code> commands.
</div><div class="important"><h2>Important</h2><div class="para">
Programs that do not require access to the shell, such as email clients or the <code class="command">sudo</code> command, can still access the root account.
</div></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Disallowing_Root_Access-Disabling_Root_Logins">2.1.4.2.2. Disabling Root Logins</h5></div></div></div><a id="d0e3023" class="indexterm"/><div class="para">
To further limit access to the root account, administrators can disable root logins at the console by editing the <code class="filename">/etc/securetty</code> file. This file lists all devices the root user is allowed to log into. If the file does not exist at all, the root user can log in through any communication device on the system, whether via the console or a raw network interface. This is dangerous, because a user can log in to his machine as root via Telnet, which transmits the password in plain text over the network. By default, Fedora's <code class="filename">/etc/securetty</code> file only allows the root user to log in at the console physically attached to the machine. To prevent root from logging in, remove the contents of this file by typing the following command:
</div><pre class="screen"><code class="command">echo > /etc/securetty</code>
</pre><div class="warning"><h2>Warning</h2><div class="para">
A blank <code class="filename">/etc/securetty</code> file does <span class="emphasis"><em>not</em></span> prevent the root user from logging in remotely using the OpenSSH suite of tools because the console is not opened until after authentication.
</div></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Disallowing_Root_Access-Disabling_Root_SSH_Logins">2.1.4.2.3. Disabling Root SSH Logins</h5></div></div></div><a id="d0e3056" class="indexterm"/><div class="para">
To prevent root logins via the SSH protocol, edit the SSH daemon's configuration file (<code class="filename">/etc/ssh/sshd_config</code>). Change the line that reads:
</div><pre class="screen"><code class="computeroutput"># PermitRootLogin yes</code>
</pre><div class="para">
to read as follows:
</div><pre class="screen"><code class="computeroutput"> PermitRootLogin no</code>
</pre></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Disallowing_Root_Access-Disabling_Root_Using_PAM">2.1.4.2.4. Disabling Root Using PAM</h5></div></div></div><a id="d0e3081" class="indexterm"/><div class="para">
PAM, through the <code class="filename">/lib/security/pam_listfile.so</code> module, allows great flexibility in denying specific accounts. The administrator can use this module to reference a list of users who are not allowed to log in. Below is an example of how the module is used for the <code class="command">vsftpd</code> FTP server in the <code class="filename">/etc/pam.d/vsftpd</code> PAM configuration file (the <code class="computeroutput">\</code> character at the end of the first line in the following example is <span class="emphasis"><em>not</em></span> necessary if the directive is on one line):
</div><pre class="screen"><code class="computeroutput">auth required /lib/security/pam_listfile.so item=user \ sense=deny file=/etc/vsftpd.ftpusers onerr=succeed</code>
</pre><div class="para">
This instructs PAM to consult the <code class="filename">/etc/vsftpd.ftpusers</code> file and deny access to the service for any listed user. The administrator can change the name of this file, and can keep separate lists for each service or use one central list to deny access to multiple services.
</div><div class="para">
If the administrator wants to deny access to multiple services, a similar line can be added to the PAM configuration files, such as <code class="filename">/etc/pam.d/pop</code> and <code class="filename">/etc/pam.d/imap</code> for mail clients, or <code class="filename">/etc/pam.d/ssh</code> for SSH clients.
</div><div class="para">
For more information about PAM, refer to <a class="xref" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM.html" title="2.4. Pluggable Authentication Modules (PAM)">Section 2.4, “Pluggable Authentication Modules (PAM)”</a>.
</div></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Administrative_Controls-Limiting_Root_Access">2.1.4.3. Limiting Root Access</h4></div></div></div><a id="d0e3132" class="indexterm"/><div class="para">
Rather than completely denying access to the root user, the administrator may want to allow access only via setuid programs, such as <code class="command">su</code> or <code class="command">sudo</code>.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Limiting_Root_Access-The_su_Command">2.1.4.3.1. The <code class="command">su</code> Command</h5></div></div></div><a id="d0e3151" class="indexterm"/><a id="d0e3160" class="indexterm"/><div class="para">
When a user executes the <code class="command">su</code> command, they are prompted for the root password and, after authentication, is given a root shell prompt.
</div><div class="para">
Once logged in via the <code class="command">su</code> command, the user <span class="emphasis"><em>is</em></span> the root user and has absolute administrative access to the system<sup>[<a id="d0e3179" href="#ftn.d0e3179" class="footnote">7</a>]</sup>. In addition, once a user has become root, it is possible for them to use the <code class="command">su</code> command to change to any other user on the system without being prompted for a password.
</div><div class="para">
Because this program is so powerful, administrators within an organization may wish to limit who has access to the command.
</div><div class="para">
One of the simplest ways to do this is to add users to the special administrative group called <em class="firstterm">wheel</em>. To do this, type the following command as root:
</div><pre class="screen"><code class="command">usermod -G wheel <em class="replaceable"><code><username></code></em></code>
</pre><div class="para">
In the previous command, replace <em class="replaceable"><code><username></code></em> with the username you want to add to the <code class="command">wheel</code> group.
</div><a id="d0e3207" class="indexterm"/><div class="para">
You can also use the <span class="application"><strong>User Manager</strong></span> to modify group memberships, as follows. Note: you need Administrator privileges to perform this procedure.
</div><div class="procedure"><ol class="1"><li><div class="para">
Click the <span class="guimenu"><strong>System</strong></span> menu on the Panel, point to <span class="guisubmenu"><strong>Administration</strong></span> and then click <span class="guimenuitem"><strong>Users and Groups</strong></span> to display the User Manager. Alternatively, type the command <code class="command">system-config-users</code> at a shell prompt.
</div></li><li><div class="para">
Click the <span class="guilabel"><strong>Users</strong></span> tab, and select the required user in the list of users.
</div></li><li><div class="para">
Click <span class="guibutton"><strong>Properties</strong></span> on the toolbar to display the User Properties dialog box (or choose <span class="guimenuitem"><strong>Properties</strong></span> on the <span class="guimenu"><strong>File</strong></span> menu).
</div></li><li><div class="para">
Click the <span class="guilabel"><strong>Groups</strong></span> tab, select the check box for the wheel group, and then click <span class="guibutton"><strong>OK</strong></span>. Refer to <a class="xref" href="chap-Security_Guide-Securing_Your_Network.html#figu-Security_Guide-The_su_Command-Adding_users_to_the_wheel_group." title="Figure 2.2. Adding users to the "wheel" group.">Figure 2.2, “Adding users to the "wheel" group.”</a>.
</div></li><li><div class="para">
Open the PAM configuration file for <code class="command">su</code> (<code class="filename">/etc/pam.d/su</code>) in a text editor and remove the comment <span class="keycap"><strong>#</strong></span> from the following line:
</div><pre class="screen">auth required /lib/security/$ISA/pam_wheel.so use_uid
</pre><div class="para">
This change means that only members of the administrative group <code class="computeroutput">wheel</code> can use this program.
</div></li></ol></div><div class="figure" id="figu-Security_Guide-The_su_Command-Adding_users_to_the_wheel_group."><div class="figure-contents"><div class="mediaobject"><img src="images/user_pass_groups.png" alt="Adding users to the "wheel" group."/><div class="longdesc"><div class="para">
<span class="guilabel"><strong>Groups</strong></span> pane illustration
</div></div></div></div><h6>Figure 2.2. Adding users to the "wheel" group.</h6></div><br class="figure-break"/><div class="note"><h2>Note</h2><div class="para">
The root user is part of the <code class="computeroutput">wheel</code> group by default.
</div></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Limiting_Root_Access-The_sudo_Command">2.1.4.3.2. The <code class="command">sudo</code> Command</h5></div></div></div><a id="d0e3311" class="indexterm"/><a id="d0e3320" class="indexterm"/><div class="para">
The <code class="command">sudo</code> command offers another approach to giving users administrative access. When trusted users precede an administrative command with <code class="command">sudo</code>, they are prompted for <span class="emphasis"><em>their own</em></span> password. Then, when they have been authenticated and assuming that the command is permitted, the administrative command is executed as if they were the root user.
</div><div class="para">
The basic format of the <code class="command">sudo</code> command is as follows:
</div><pre class="screen"><code class="command">sudo <em class="replaceable"><code><command></code></em></code>
</pre><div class="para">
In the above example, <em class="replaceable"><code><command></code></em> would be replaced by a command normally reserved for the root user, such as <code class="command">mount</code>.
</div><div class="important"><h2>Important</h2><div class="para">
Users of the <code class="command">sudo</code> command should take extra care to log out before walking away from their machines since sudoers can use the command again without being asked for a password within a five minute period. This setting can be altered via the configuration file, <code class="filename">/etc/sudoers</code>.
</div></div><div class="para">
The <code class="command">sudo</code> command allows for a high degree of flexibility. For instance, only users listed in the <code class="filename">/etc/sudoers</code> configuration file are allowed to use the <code class="command">sudo</code> command and the command is executed in <span class="emphasis"><em>the user's</em></span> shell, not a root shell. This means the root shell can be completely disabled, as shown in <a class="xref" href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Disallowing_Root_Access-Disabling_the_Root_Shell" title="2.1.4.2.1. Disabling the Root Shell">Section 2.1.4.2.1, “Disabling the Root Shell”</a>.
</div><div class="para">
The <code class="command">sudo</code> command also provides a comprehensive audit trail. Each successful authentication is logged to the file <code class="filename">/var/log/messages</code> and the command issued along with the issuer's user name is logged to the file <code class="filename">/var/log/secure</code>.
</div><div class="para">
Another advantage of the <code class="command">sudo</code> command is that an administrator can allow different users access to specific commands based on their needs.
</div><div class="para">
Administrators wanting to edit the <code class="command">sudo</code> configuration file, <code class="filename">/etc/sudoers</code>, should use the <code class="command">visudo</code> command.
</div><div class="para">
To give someone full administrative privileges, type <code class="command">visudo</code> and add a line similar to the following in the user privilege specification section:
</div><pre class="screen"><code class="command">juan ALL=(ALL) ALL</code>
</pre><div class="para">
This example states that the user, <code class="computeroutput">juan</code>, can use <code class="command">sudo</code> from any host and execute any command.
</div><div class="para">
The example below illustrates the granularity possible when configuring <code class="command">sudo</code>:
</div><pre class="screen"><code class="command">%users localhost=/sbin/shutdown -h now</code>
</pre><div class="para">
This example states that any user can issue the command <code class="command">/sbin/shutdown -h now</code> as long as it is issued from the console.
</div><div class="para">
The man page for <code class="filename">sudoers</code> has a detailed listing of options for this file.
</div></div></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Workstation_Security-Available_Network_Services">2.1.5. Available Network Services</h3></div></div></div><a id="d0e3449" class="indexterm"/><div class="para">
While user access to administrative controls is an important issue for system administrators within an organization, monitoring which network services are active is of paramount importance to anyone who administers and operates a Linux system.
</div><div class="para">
Many services under Fedora behave as network servers. If a network service is running on a machine, then a server application (called a <em class="firstterm">daemon</em>), is listening for connections on one or more network ports. Each of these servers should be treated as a potential avenue of attack.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Available_Network_Services-Risks_To_Services">2.1.5.1. Risks To Services</h4></div></div></div><a id="d0e3462" class="indexterm"/><a id="d0e3467" class="indexterm"/><a id="d0e3474" class="indexterm"/><a id="d0e3481" class="indexterm"/><div class="para">
Network services can pose many risks for Linux systems. Below is a list of some of the primary issues:
</div><div class="itemizedlist"><ul><li><div class="para">
<span class="emphasis"><em>Denial of Service Attacks (DoS)</em></span> — By flooding a service with requests, a denial of service attack can render a system unusable as it tries to log and answer each request.
</div></li><li><div class="para">
<span class="emphasis"><em>Script Vulnerability Attacks</em></span> — If a server is using scripts to execute server-side actions, as Web servers commonly do, a cracker can attack improperly written scripts. These script vulnerability attacks can lead to a buffer overflow condition or allow the attacker to alter files on the system.
</div></li><li><div class="para">
<span class="emphasis"><em>Buffer Overflow Attacks</em></span> — Services that connect to ports numbered 0 through 1023 must run as an administrative user. If the application has an exploitable buffer overflow, an attacker could gain access to the system as the user running the daemon. Because exploitable buffer overflows exist, crackers use automated tools to identify systems with vulnerabilities, and once they have gained access, they use automated rootkits to maintain their access to the system.
</div></li></ul></div><a id="d0e3509" class="indexterm"/><div class="note"><h2>Note</h2><div class="para">
The threat of buffer overflow vulnerabilities is mitigated in Fedora by <em class="firstterm">ExecShield</em>, an executable memory segmentation and protection technology supported by x86-compatible uni- and multi-processor kernels. ExecShield reduces the risk of buffer overflow by separating virtual memory into executable and non-executable segments. Any program code that tries to execute outside of the executable segment (such as malicious code injected from a buffer overflow exploit) triggers a segmentation fault and terminates.
</div><div class="para">
Execshield also includes support for <em class="firstterm">No eXecute</em> (<acronym class="acronym">NX</acronym>) technology on AMD64 platforms and <em class="firstterm">eXecute Disable</em> (<acronym class="acronym">XD</acronym>) technology on Itanium and <span class="trademark">Intel</span>® 64 systems. These technologies work in conjunction with ExecShield to prevent malicious code from running in the executable portion of virtual memory with a granularity of 4KB of executable code, lowering the risk of attack from stealthy buffer overflow exploits.
</div></div><div class="tip"><h2>Tip</h2><div class="para">
To limit exposure to attacks over the network, all services that are unused should be turned off.
</div></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Available_Network_Services-Identifying_and_Configuring_Services">2.1.5.2. Identifying and Configuring Services</h4></div></div></div><a id="d0e3549" class="indexterm"/><a id="d0e3554" class="indexterm"/><a id="d0e3558" class="indexterm"/><a id="d0e3562" class="indexterm"/><a id="d0e3566" class="indexterm"/><a id="d0e3570" class="indexterm"/><a id="d0e3574" class="indexterm"/><div class="para">
To enhance security, most network services installed with Fedora are turned off by default. There are, however, some notable exceptions:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="command">cupsd</code> — The default print server for Fedora.
</div></li><li><div class="para">
<code class="command">lpd</code> — An alternative print server.
</div></li><li><div class="para">
<code class="command">xinetd</code> — A super server that controls connections to a range of subordinate servers, such as <code class="command">gssftp</code> and <code class="command">telnet</code>.
</div></li><li><div class="para">
<code class="command">sendmail</code> — The Sendmail <em class="firstterm">Mail Transport Agent</em> (<abbr class="abbrev">MTA</abbr>) is enabled by default, but only listens for connections from the <span class="interface">localhost</span>.
</div></li><li><div class="para">
<code class="command">sshd</code> — The OpenSSH server, which is a secure replacement for Telnet.
</div></li></ul></div><div class="para">
When determining whether to leave these services running, it is best to use common sense and err on the side of caution. For example, if a printer is not available, do not leave <code class="command">cupsd</code> running. The same is true for <code class="command">portmap</code>. If you do not mount NFSv3 volumes or use NIS (the <code class="command">ypbind</code> service), then <code class="command">portmap</code> should be disabled.
</div><a id="d0e3640" class="indexterm"/><div class="figure" id="figu-Security_Guide-Identifying_and_Configuring_Services-Services_Configuration_Tool"><div class="figure-contents"><div class="mediaobject"><img src="images/serv-config.png" alt="Services Configuration Tool"/><div class="longdesc"><div class="para">
<span class="application"><strong>Services Configuration Tool</strong></span> illustration
</div></div></div></div><h6>Figure 2.3. <span class="application">Services Configuration Tool</span></h6></div><br class="figure-break"/><div class="para">
If unsure of the purpose for a particular service, the <span class="application"><strong>Services Configuration Tool</strong></span> has a description field, illustrated in <a class="xref" href="chap-Security_Guide-Securing_Your_Network.html#figu-Security_Guide-Identifying_and_Configuring_Services-Services_Configuration_Tool" title="Figure 2.3. Services Configuration Tool">Figure 2.3, “Services Configuration Tool”</a>, that provides additional information.
</div><div class="para">
Checking which network services are available to start at boot time is only part of the story. You should also check which ports are open and listening. Refer to <a class="xref" href="sect-Security_Guide-Server_Security-Verifying_Which_Ports_Are_Listening.html" title="2.2.8. Verifying Which Ports Are Listening">Section 2.2.8, “Verifying Which Ports Are Listening”</a> for more information.
</div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Available_Network_Services-Insecure_Services">2.1.5.3. Insecure Services</h4></div></div></div><a id="d0e3671" class="indexterm"/><div class="para">
Potentially, any network service is insecure. This is why turning off unused services is so important. Exploits for services are routinely revealed and patched, making it very important to regularly update packages associated with any network service. Refer to <a class="xref" href="sect-Security_Guide-Security_Updates.html" title="1.5. Security Updates">Section 1.5, “Security Updates”</a> for more information.
</div><div class="para">
Some network protocols are inherently more insecure than others. These include any services that:
</div><div class="itemizedlist"><ul><li><div class="para">
<span class="emphasis"><em>Transmit Usernames and Passwords Over a Network Unencrypted</em></span> — Many older protocols, such as Telnet and FTP, do not encrypt the authentication session and should be avoided whenever possible.
</div></li><li><div class="para">
<span class="emphasis"><em>Transmit Sensitive Data Over a Network Unencrypted</em></span> — Many protocols transmit data over the network unencrypted. These protocols include Telnet, FTP, HTTP, and SMTP. Many network file systems, such as NFS and SMB, also transmit information over the network unencrypted. It is the user's responsibility when using these protocols to limit what type of data is transmitted.
</div><div class="para">
Remote memory dump services, like <code class="command">netdump</code>, transmit the contents of memory over the network unencrypted. Memory dumps can contain passwords or, even worse, database entries and other sensitive information.
</div><div class="para">
Other services like <code class="command">finger</code> and <code class="command">rwhod</code> reveal information about users of the system.
</div></li></ul></div><div class="para">
Examples of inherently insecure services include <code class="command">rlogin</code>, <code class="command">rsh</code>, <code class="command">telnet</code>, and <code class="command">vsftpd</code>.
</div><a id="d0e3720" class="indexterm"/><a id="d0e3725" class="indexterm"/><a id="d0e3730" class="indexterm"/><div class="para">
All remote login and shell programs (<code class="command">rlogin</code>, <code class="command">rsh</code>, and <code class="command">telnet</code>) should be avoided in favor of SSH. Refer to <a class="xref" href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security-Security_Enhanced_Communication_Tools" title="2.1.7. Security Enhanced Communication Tools">Section 2.1.7, “Security Enhanced Communication Tools”</a> for more information about <code class="command">sshd</code>.
</div><div class="para">
FTP is not as inherently dangerous to the security of the system as remote shells, but FTP servers must be carefully configured and monitored to avoid problems. Refer to <a class="xref" href="sect-Security_Guide-Server_Security-Securing_FTP.html" title="2.2.6. Securing FTP">Section 2.2.6, “Securing FTP”</a> for more information about securing FTP servers.
</div><div class="para">
Services that should be carefully implemented and behind a firewall include:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="command">finger</code>
</div></li><li><div class="para">
<code class="command">authd</code> (this was called <code class="command">identd</code> in previous Fedora releases.)
</div></li><li><div class="para">
<code class="command">netdump</code>
</div></li><li><div class="para">
<code class="command">netdump-server</code>
</div></li><li><div class="para">
<code class="command">nfs</code>
</div></li><li><div class="para">
<code class="command">rwhod</code>
</div></li><li><div class="para">
<code class="command">sendmail</code>
</div></li><li><div class="para">
<code class="command">smb</code> (Samba)
</div></li><li><div class="para">
<code class="command">yppasswdd</code>
</div></li><li><div class="para">
<code class="command">ypserv</code>
</div></li><li><div class="para">
<code class="command">ypxfrd</code>
</div></li></ul></div><div class="para">
More information on securing network services is available in <a class="xref" href="sect-Security_Guide-Server_Security.html" title="2.2. Server Security">Section 2.2, “Server Security”</a>.
</div><div class="para">
The next section discusses tools available to set up a simple firewall.
</div></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Workstation_Security-Personal_Firewalls">2.1.6. Personal Firewalls</h3></div></div></div><a id="d0e3836" class="indexterm"/><div class="para">
After the <span class="emphasis"><em>necessary</em></span> network services are configured, it is important to implement a firewall.
</div><div class="important"><h2>Important</h2><div class="para">
You should configure the necessary services and implement a firewall <span class="emphasis"><em>before</em></span> connecting to the Internet or any other network that you do not trust.
</div></div><div class="para">
Firewalls prevent network packets from accessing the system's network interface. If a request is made to a port that is blocked by a firewall, the request is ignored. If a service is listening on one of these blocked ports, it does not receive the packets and is effectively disabled. For this reason, care should be taken when configuring a firewall to block access to ports not in use, while not blocking access to ports used by configured services.
</div><div class="para">
For most users, the best tool for configuring a simple firewall is the graphical firewall configuration tool which ships with Fedora: the <span class="application"><strong>Security Level Configuration Tool</strong></span> (<code class="command">system-config-securitylevel</code>). This tool creates broad <code class="command">iptables</code> rules for a general-purpose firewall using a control panel interface.
</div><div class="para">
Refer to <a class="xref" href="sect-Security_Guide-Firewalls-Basic_Firewall_Configuration.html" title="2.8.2. Basic Firewall Configuration">Section 2.8.2, “Basic Firewall Configuration”</a> for more information about using this application and its available options.
</div><div class="para">
For advanced users and server administrators, manually configuring a firewall with <code class="command">iptables</code> is probably a better option. Refer to <a class="xref" href="sect-Security_Guide-Firewalls.html" title="2.8. Firewalls">Section 2.8, “Firewalls”</a> for more information. Refer to <a class="xref" href="sect-Security_Guide-IPTables.html" title="2.9. IPTables">Section 2.9, “IPTables”</a> for a comprehensive guide to the <code class="command">iptables</code> command.
</div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Workstation_Security-Security_Enhanced_Communication_Tools">2.1.7. Security Enhanced Communication Tools</h3></div></div></div><a id="d0e3886" class="indexterm"/><a id="d0e3891" class="indexterm"/><a id="d0e3898" class="indexterm"/><div class="para">
As the size and popularity of the Internet has grown, so has the threat of communication interception. Over the years, tools have been developed to encrypt communications as they are transferred over the network.
</div><div class="para">
Fedora ships with two basic tools that use high-level, public-key-cryptography-based encryption algorithms to protect information as it travels over the network.
</div><div class="itemizedlist"><ul><li><div class="para">
<span class="emphasis"><em>OpenSSH</em></span> — A free implementation of the SSH protocol for encrypting network communication.
</div></li><li><div class="para">
<span class="emphasis"><em>Gnu Privacy Guard (GPG)</em></span> — A free implementation of the PGP (Pretty Good Privacy) encryption application for encrypting data.
</div></li></ul></div><a id="d0e3922" class="indexterm"/><a id="d0e3925" class="indexterm"/><a id="d0e3931" class="indexterm"/><a id="d0e3937" class="indexterm"/><div class="para">
OpenSSH is a safer way to access a remote machine and replaces older, unencrypted services like <code class="command">telnet</code> and <code class="command">rsh</code>. OpenSSH includes a network service called <code class="command">sshd</code> and three command line client applications:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="command">ssh</code> — A secure remote console access client.
</div></li><li><div class="para">
<code class="command">scp</code> — A secure remote copy command.
</div></li><li><div class="para">
<code class="command">sftp</code> — A secure pseudo-ftp client that allows interactive file transfer sessions.
</div></li></ul></div><div class="important"><h2>Important</h2><div class="para">
Although the <code class="command">sshd</code> service is inherently secure, the service <span class="emphasis"><em>must</em></span> be kept up-to-date to prevent security threats. Refer to <a class="xref" href="sect-Security_Guide-Security_Updates.html" title="1.5. Security Updates">Section 1.5, “Security Updates”</a> for more information.
</div></div><div class="para">
GPG is one way to ensure private email communication. It can be used both to email sensitive data over public networks and to protect sensitive data on hard drives.
</div></div></div><div class="footnotes"><br/><hr/><div class="footnote"><p><sup>[<a id="ftn.d0e1882" href="#d0e1882" class="para">5</a>] </sup>
Since system BIOSes differ between manufacturers, some may not support password protection of either type, while others may support one type but not the other.
</p></div><div class="footnote"><p><sup>[<a id="ftn.d0e2021" href="#d0e2021" class="para">6</a>] </sup>
GRUB also accepts unencrypted passwords, but it is recommended that an MD5 hash be used for added security.
</p></div><div class="footnote"><p><sup>[<a id="ftn.d0e3179" href="#d0e3179" class="para">7</a>] </sup>
This access is still subject to the restrictions imposed by SELinux, if it is enabled.
</p></div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Security_Updates.html"><strong>Prev</strong>1.5. Security Updates</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Server_Security.html"><strong>Next</strong>2.2. Server Security</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Chapter 1. Security Overview</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="index.html" title="Linux Security Guide"/><link rel="prev" href="We_Need_Feedback.html" title="2. We Need Feedback!"/><link rel="next" href="sect-Security_Guide-Vulnerability_Assessment.html" title="1.2. Vulnerability Assessment"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="We_Need_Feedback.html"><stro
ng>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Vulnerability_Assessment.html"><strong>Next</strong></a></li></ul><div class="chapter" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="chap-Security_Guide-Security_Overview">Chapter 1. Security Overview</h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="chap-Security_Guide-Security_Overview.html#sect-Security_Guide-Introduction_to_Security">1.1. Introduction to Security</a></span></dt><dd><dl><dt><span class="section"><a href="chap-Security_Guide-Security_Overview.html#sect-Security_Guide-Introduction_to_Security-What_is_Computer_Security">1.1.1. What is Computer Security?</a></span></dt><dt><span class="section"><a href="chap-Security_Guide-Security_Overview.html#sect-Security_Guide-Introduction_to_Security-Security_Controls">1.1.2. Security Controls</a></span></dt><dt><span class="section"><a href="chap-Security_Guide-Security_Overview.html#
sect-Security_Guide-Introduction_to_Security-Conclusion">1.1.3. Conclusion</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Vulnerability_Assessment.html">1.2. Vulnerability Assessment</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Vulnerability_Assessment.html#sect-Security_Guide-Vulnerability_Assessment-Thinking_Like_the_Enemy">1.2.1. Thinking Like the Enemy</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Vulnerability_Assessment-Defining_Assessment_and_Testing.html">1.2.2. Defining Assessment and Testing</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Vulnerability_Assessment-Evaluating_the_Tools.html">1.2.3. Evaluating the Tools</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Attackers_and_Vulnerabilities.html">1.3. Attackers and Vulnerabilities</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Attackers_and
_Vulnerabilities.html#sect-Security_Guide-Attackers_and_Vulnerabilities-A_Quick_History_of_Hackers">1.3.1. A Quick History of Hackers</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Network_Security.html">1.3.2. Threats to Network Security</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Server_Security.html">1.3.3. Threats to Server Security</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Workstation_and_Home_PC_Security.html">1.3.4. Threats to Workstation and Home PC Security</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Common_Exploits_and_Attacks.html">1.4. Common Exploits and Attacks</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Security_Updates.html">1.5. Security Updates</a></span></dt><dd><dl><dt><span class="section"><a href
="sect-Security_Guide-Security_Updates.html#sect-Security_Guide-Security_Updates-Updating_Packages">1.5.1. Updating Packages</a></span></dt></dl></dd></dl></div><a id="d0e390" class="indexterm"/><a id="d0e393" class="indexterm"/><div class="para">
Because of the increased reliance on powerful, networked computers to help run businesses and keep track of our personal information, industries have been formed around the practice of network and computer security. Enterprises have solicited the knowledge and skills of security experts to properly audit systems and tailor solutions to fit the operating requirements of the organization. Because most organizations are dynamic in nature, with workers accessing company IT resources locally and remotely, the need for secure computing environments has become more pronounced.
</div><div class="para">
Unfortunately, most organizations (as well as individual users) regard security as an afterthought, a process that is overlooked in favor of increased power, productivity, and budgetary concerns. Proper security implementation is often enacted <em class="firstterm">postmortem</em> — after an unauthorized intrusion has already occurred. Security experts agree that the right measures taken prior to connecting a site to an untrusted network, such as the Internet, is an effective means of thwarting most attempts at intrusion.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-Introduction_to_Security">1.1. Introduction to Security</h2></div></div></div><a id="d0e406" class="indexterm"/><a id="d0e409" class="indexterm"/><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Introduction_to_Security-What_is_Computer_Security">1.1.1. What is Computer Security?</h3></div></div></div><a id="d0e415" class="indexterm"/><div class="para">
Computer security is a general term that covers a wide area of computing and information processing. Industries that depend on computer systems and networks to conduct daily business transactions and access crucial information regard their data as an important part of their overall assets. Several terms and metrics have entered our daily business vocabulary, such as total cost of ownership (TCO) and quality of service (QoS). In these metrics, industries calculate aspects such as data integrity and high-availability as part of their planning and process management costs. In some industries, such as electronic commerce, the availability and trustworthiness of data can be the difference between success and failure.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-What_is_Computer_Security-How_did_Computer_Security_Come_about">1.1.1.1. How did Computer Security Come about?</h4></div></div></div><a id="d0e425" class="indexterm"/><div class="para">
Information security has evolved over the years due to the increasing reliance on public networks not to disclose personal, financial, and other restricted information. There are numerous instances such as the Mitnick and the Vladimir Levin cases that prompted organizations across all industries to rethink the way they handle information transmission and disclosure. The popularity of the Internet was one of the most important developments that prompted an intensified effort in data security.
</div><div class="para">
An ever-growing number of people are using their personal computers to gain access to the resources that the Internet has to offer. From research and information retrieval to electronic mail and commerce transaction, the Internet has been regarded as one of the most important developments of the 20th century.
</div><div class="para">
The Internet and its earlier protocols, however, were developed as a <em class="firstterm">trust-based</em> system. That is, the Internet Protocol was not designed to be secure in itself. There are no approved security standards built into the TCP/IP communications stack, leaving it open to potentially malicious users and processes across the network. Modern developments have made Internet communication more secure, but there are still several incidents that gain national attention and alert us to the fact that nothing is completely safe.
</div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-What_is_Computer_Security-Security_Today">1.1.1.2. Security Today</h4></div></div></div><a id="d0e442" class="indexterm"/><a id="d0e447" class="indexterm"/><a id="d0e452" class="indexterm"/><a id="d0e457" class="indexterm"/><div class="para">
In February of 2000, a Distributed Denial of Service (DDoS) attack was unleashed on several of the most heavily-trafficked sites on the Internet. The attack rendered yahoo.com, cnn.com, amazon.com, fbi.gov, and several other sites completely unreachable to normal users, as it tied up routers for several hours with large-byte ICMP packet transfers, also called a <em class="firstterm">ping flood</em>. The attack was brought on by unknown assailants using specially created, widely available programs that scanned vulnerable network servers, installed client applications called <em class="firstterm">trojans</em> on the servers, and timed an attack with every infected server flooding the victim sites and rendering them unavailable. Many blame the attack on fundamental flaws in the way routers and the protocols used are structured to accept all incoming data, no matter where or for what purpose the packets are sent.
</div><div class="para">
Currently, an estimated 945 million people use or have used the Internet worldwide (Computer Industry Almanac, 2004). At the same time:
</div><div class="itemizedlist"><ul><li><div class="para">
On any given day, there are approximately 225 major incidences of security breach reported to the CERT Coordination Center at Carnegie Mellon University.<sup>[<a id="d0e476" href="#ftn.d0e476" class="footnote">1</a>]</sup>
</div></li><li><div class="para">
In 2003, the number of CERT reported incidences jumped to 137,529 from 82,094 in 2002 and from 52,658 in 2001.<sup>[<a id="d0e486" href="#ftn.d0e486" class="footnote">2</a>]</sup>
</div></li><li><div class="para">
The worldwide economic impact of the three most dangerous Internet Viruses of the last three years was estimated at US$13.2 Billion.<sup>[<a id="d0e496" href="#ftn.d0e496" class="footnote">3</a>]</sup>
</div></li></ul></div><div class="para">
Computer security has become a quantifiable and justifiable expense for all IT budgets. Organizations that require data integrity and high availability elicit the skills of system administrators, developers, and engineers to ensure 24x7 reliability of their systems, services, and information. Falling victim to malicious users, processes, or coordinated attacks is a direct threat to the success of the organization.
</div><div class="para">
Unfortunately, system and network security can be a difficult proposition, requiring an intricate knowledge of how an organization regards, uses, manipulates, and transmits its information. Understanding the way an organization (and the people that make up the organization) conducts business is paramount to implementing a proper security plan.
</div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-What_is_Computer_Security-Standardizing_Security">1.1.1.3. Standardizing Security</h4></div></div></div><div class="para">
Enterprises in every industry rely on regulations and rules that are set by standards making bodies such as the American Medical Association (AMA) or the Institute of Electrical and Electronics Engineers (IEEE). The same ideals hold true for information security. Many security consultants and vendors agree upon the standard security model known as CIA, or <em class="firstterm">Confidentiality, Integrity, and Availability</em>. This three-tiered model is a generally accepted component to assessing risks of sensitive information and establishing security policy. The following describes the CIA model in further detail:
</div><div class="itemizedlist"><ul><li><div class="para">
Confidentiality — Sensitive information must be available only to a set of pre-defined individuals. Unauthorized transmission and usage of information should be restricted. For example, confidentiality of information ensures that a customer's personal or financial information is not obtained by an unauthorized individual for malicious purposes such as identity theft or credit fraud.
</div></li><li><div class="para">
Integrity — Information should not be altered in ways that render it incomplete or incorrect. Unauthorized users should be restricted from the ability to modify or destroy sensitive information.
</div></li><li><div class="para">
Availability — Information should be accessible to authorized users any time that it is needed. Availability is a warranty that information can be obtained with an agreed-upon frequency and timeliness. This is often measured in terms of percentages and agreed to formally in Service Level Agreements (SLAs) used by network service providers and their enterprise clients.
</div></li></ul></div></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Introduction_to_Security-Security_Controls">1.1.2. Security Controls</h3></div></div></div><a id="d0e528" class="indexterm"/><a id="d0e535" class="indexterm"/><div class="para">
Computer security is often divided into three distinct master categories, commonly referred to as <em class="wordasword">controls</em>:
</div><div class="itemizedlist"><ul><li><div class="para">
Physical
</div></li><li><div class="para">
Technical
</div></li><li><div class="para">
Administrative
</div></li></ul></div><div class="para">
These three broad categories define the main objectives of proper security implementation. Within these controls are sub-categories that further detail the controls and how to implement them.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Security_Controls-Physical_Controls">1.1.2.1. Physical Controls</h4></div></div></div><a id="d0e558" class="indexterm"/><div class="para">
Physical control is the implementation of security measures in a defined structure used to deter or prevent unauthorized access to sensitive material. Examples of physical controls are:
</div><div class="itemizedlist"><ul><li><div class="para">
Closed-circuit surveillance cameras
</div></li><li><div class="para">
Motion or thermal alarm systems
</div></li><li><div class="para">
Security guards
</div></li><li><div class="para">
Picture IDs
</div></li><li><div class="para">
Locked and dead-bolted steel doors
</div></li><li><div class="para">
Biometrics (includes fingerprint, voice, face, iris, handwriting, and other automated methods used to recognize individuals)
</div></li></ul></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Security_Controls-Technical_Controls">1.1.2.2. Technical Controls</h4></div></div></div><a id="d0e587" class="indexterm"/><div class="para">
Technical controls use technology as a basis for controlling the access and usage of sensitive data throughout a physical structure and over a network. Technical controls are far-reaching in scope and encompass such technologies as:
</div><div class="itemizedlist"><ul><li><div class="para">
Encryption
</div></li><li><div class="para">
Smart cards
</div></li><li><div class="para">
Network authentication
</div></li><li><div class="para">
Access control lists (ACLs)
</div></li><li><div class="para">
File integrity auditing software
</div></li></ul></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Security_Controls-Administrative_Controls">1.1.2.3. Administrative Controls</h4></div></div></div><a id="d0e613" class="indexterm"/><div class="para">
Administrative controls define the human factors of security. It involves all levels of personnel within an organization and determines which users have access to what resources and information by such means as:
</div><div class="itemizedlist"><ul><li><div class="para">
Training and awareness
</div></li><li><div class="para">
Disaster preparedness and recovery plans
</div></li><li><div class="para">
Personnel recruitment and separation strategies
</div></li><li><div class="para">
Personnel registration and accounting
</div></li></ul></div></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Introduction_to_Security-Conclusion">1.1.3. Conclusion</h3></div></div></div><a id="d0e636" class="indexterm"/><div class="para">
Now that you have learned about the origins, reasons, and aspects of security, you can determine the appropriate course of action with regard to Fedora. It is important to know what factors and conditions make up security in order to plan and implement a proper strategy. With this information in mind, the process can be formalized and the path becomes clearer as you delve deeper into the specifics of the security process.
</div></div></div><div class="footnotes"><br/><hr/><div class="footnote"><p><sup>[<a id="ftn.d0e476" href="#d0e476" class="para">1</a>] </sup>
Source: <a href="http://www.cert.org">http://www.cert.org</a>
</p></div><div class="footnote"><p><sup>[<a id="ftn.d0e486" href="#d0e486" class="para">2</a>] </sup>
Source: <a href="http://www.cert.org/stats/">http://www.cert.org/stats/</a>
</p></div><div class="footnote"><p><sup>[<a id="ftn.d0e496" href="#d0e496" class="para">3</a>] </sup>
Source: <a href="http://www.newsfactor.com/perl/story/16407.html">http://www.newsfactor.com/perl/story/16407.html</a>
</p></div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="We_Need_Feedback.html"><strong>Prev</strong>2. We Need Feedback!</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Vulnerability_Assessment.html"><strong>Next</strong>1.2. Vulnerability Assessment</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Chapter 6. Software Maintenance</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="index.html" title="Linux Security Guide"/><link rel="prev" href="sect-Security_Guide-Secure_Installation-Utilize_LUKS_Partition_Encryption.html" title="5.2. Utilize LUKS Partition Encryption"/><link rel="next" href="sect-Security_Guide-Software_Maintenance-Plan_and_Configure_Security_Updates.html" title="6.2. Plan and Configure Security Updates"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt=
"Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Secure_Installation-Utilize_LUKS_Partition_Encryption.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Software_Maintenance-Plan_and_Configure_Security_Updates.html"><strong>Next</strong></a></li></ul><div class="chapter" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="chap-Security_Guide-Software_Maintenance">Chapter 6. Software Maintenance</h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="chap-Security_Guide-Software_Maintenance.html#sect-Security_Guide-Software_Maintenance-Install_Minimal_Software">6.1. Install Minimal Software</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Software_Maintenance-Plan_and_Configure_Security_Updates.html">6.2. Plan and Configure Security Updates</a></span></dt><dt><span class="section"><a href="sect-Security_Guid
e-Software_Maintenance-Plan_and_Configure_Security_Updates-Adjusting_Automatic_Updates.html">6.3. Adjusting Automatic Updates</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Software_Maintenance-Install_Signed_Packages_from_Well_Known_Repositories.html">6.4. Install Signed Packages from Well Known Repositories</a></span></dt></dl></div><div class="para">
Software maintenance is extremely important to maintaining a secure system. It is vital to patch software as soon as it becomes available in order to prevent attackers from using known holes to infiltrate your system.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-Software_Maintenance-Install_Minimal_Software">6.1. Install Minimal Software</h2></div></div></div><div class="para">
It is best practice to install only the packages you will use because each piece of software on your computer could possibly contain a vulnerability. If you are installing from the DVD media take the opportunity to select exactly what packages you want to install during the installation. When you find you need another package, you can always add it to the system later.
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Linux Security Guide</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><meta name="description" content="The Linux Security Guide is designed to assist users of Linux in learning the processes and practices of securing workstations and servers against local and remote intrusion, exploitation, and malicious activity. The Linux Security Guide details the planning and the tools involved in creating a secured computing environment for the data center, workplace, and home. With proper administrative knowledge, vigilance, and tools, systems running Linux can be both fully functional and secured from most common intrusion and exploit methods."/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="next" href="pref-Security_Guide-Preface.html" title="Pref
ace"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"/><li class="next"><a accesskey="n" href="pref-Security_Guide-Preface.html"><strong>Next</strong></a></li></ul><div class="book" lang="en-US"><div class="titlepage"><div><div class="producttitle"><span class="productname">fedora</span> <span class="productnumber">10</span></div><div><h1 id="d0e1" class="title">Linux Security Guide</h1></div><div><h2 class="subtitle">A Guide to Securing Linux</h2></div><p class="edition">Edition 1.0</p><div><h3 class="corpauthor">
<span class="inlinemediaobject"><object type="image/svg+xml" data="Common_Content/images/title_logo.svg"/></span>
</h3></div><div><div class="authorgroup"><div class="author"><h3 class="author"><span class="firstname">Johnray</span> <span class="surname">Fuller</span></h3><div class="affiliation"><span class="orgname">Red Hat</span></div><code class="email"><a class="email" href="mailto:jrfuller@redhat.com">jrfuller(a)redhat.com</a></code></div><div class="author"><h3 class="author"><span class="firstname">John</span> <span class="surname">Ha</span></h3><div class="affiliation"><span class="orgname">Red Hat</span></div><code class="email"><a class="email" href="mailto:jha@redhat.com">jha(a)redhat.com</a></code></div><div class="author"><h3 class="author"><span class="firstname">David</span> <span class="surname">O'Brien</span></h3><div class="affiliation"><span class="orgname">Red Hat</span></div><code class="email"><a class="email" href="mailto:daobrien@redhat.com">daobrien(a)redhat.com</a></code></div><div class="author"><h3 class="author"><span class="firstname">Eric</span> <span class="
surname">Christensen</span></h3><div class="affiliation"><span class="orgname">Fedora Project</span> <span class="orgdiv">Documentation Team</span></div><code class="email"><a class="email" href="mailto:sparks@fedoraproject.org">sparks(a)fedoraproject.org</a></code></div></div></div><hr/><div><div id="d0e27" class="legalnotice"><h1 class="legalnotice">Legal Notice</h1><div class="para">
Copyright <span class="trademark"/>© 2008 Red Hat, Inc. This material may only be distributed subject to the terms and conditions set forth in the Open Publication License, V1.0, (the latest version is presently available at <a href="http://www.opencontent.org/openpub/">http://www.opencontent.org/openpub/</a>).
</div><div class="para">
Fedora and the Fedora Infinity Design logo are trademarks or registered trademarks of Red Hat, Inc., in the U.S. and other countries.
</div><div class="para">
Red Hat and the Red Hat "Shadow Man" logo are registered trademarks of Red Hat Inc. in the United States and other countries.
</div><div class="para">
All other trademarks and copyrights referred to are the property of their respective owners.
</div><div class="para">
Documentation, as with software itself, may be subject to export control. Read about Fedora Project export controls at <a href="http://fedoraproject.org/wiki/Legal/Export">http://fedoraproject.org/wiki/Legal/Export</a>.
</div></div></div><div><div class="abstract"><h6>Abstract</h6><div class="para">The Linux Security Guide is designed to assist users of Linux in
learning the processes and practices of securing workstations and
servers against local and remote intrusion, exploitation, and
malicious activity. The Linux Security Guide details the planning
and the tools involved in creating a secured computing environment
for the data center, workplace, and home. With proper
administrative knowledge, vigilance, and tools, systems running
Linux can be both fully functional and secured from most common
intrusion and exploit methods.</div></div></div></div><hr/></div><div class="toc"><dl><dt><span class="preface"><a href="pref-Security_Guide-Preface.html">Preface</a></span></dt><dd><dl><dt><span class="section"><a href="pref-Security_Guide-Preface.html#d0e91">1. Document Conventions</a></span></dt><dd><dl><dt><span class="section"><a href="pref-Security_Guide-Preface.html#d0e101">1.1. Typographic Conventions</a></span></dt><dt><span class="section"><a href="pref-Security_Guide-Preface.html#d0e317">1.2. Pull-quote Conventions</a></span></dt><dt><span class="section"><a href="pref-Security_Guide-Preface.html#d0e336">1.3. Notes and Warnings</a></span></dt></dl></dd><dt><span class="section"><a href="We_Need_Feedback.html">2. We Need Feedback!</a></span></dt></dl></dd><dt><span class="chapter"><a href="chap-Security_Guide-Security_Overview.html">1. Security Overview</a></span></dt><dd><dl><dt><span class="section"><a href="chap-Security_Guide-Security_Overview.html#sect-Security
_Guide-Introduction_to_Security">1.1. Introduction to Security</a></span></dt><dd><dl><dt><span class="section"><a href="chap-Security_Guide-Security_Overview.html#sect-Security_Guide-Introduction_to_Security-What_is_Computer_Security">1.1.1. What is Computer Security?</a></span></dt><dt><span class="section"><a href="chap-Security_Guide-Security_Overview.html#sect-Security_Guide-Introduction_to_Security-Security_Controls">1.1.2. Security Controls</a></span></dt><dt><span class="section"><a href="chap-Security_Guide-Security_Overview.html#sect-Security_Guide-Introduction_to_Security-Conclusion">1.1.3. Conclusion</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Vulnerability_Assessment.html">1.2. Vulnerability Assessment</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Vulnerability_Assessment.html#sect-Security_Guide-Vulnerability_Assessment-Thinking_Like_the_Enemy">1.2.1. Thinking Like the Enemy</a></span></dt><dt>
<span class="section"><a href="sect-Security_Guide-Vulnerability_Assessment-Defining_Assessment_and_Testing.html">1.2.2. Defining Assessment and Testing</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Vulnerability_Assessment-Evaluating_the_Tools.html">1.2.3. Evaluating the Tools</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Attackers_and_Vulnerabilities.html">1.3. Attackers and Vulnerabilities</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Attackers_and_Vulnerabilities.html#sect-Security_Guide-Attackers_and_Vulnerabilities-A_Quick_History_of_Hackers">1.3.1. A Quick History of Hackers</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Network_Security.html">1.3.2. Threats to Network Security</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Server_Security.html">1.3.3. T
hreats to Server Security</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Workstation_and_Home_PC_Security.html">1.3.4. Threats to Workstation and Home PC Security</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Common_Exploits_and_Attacks.html">1.4. Common Exploits and Attacks</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Security_Updates.html">1.5. Security Updates</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Security_Updates.html#sect-Security_Guide-Security_Updates-Updating_Packages">1.5.1. Updating Packages</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="chap-Security_Guide-Securing_Your_Network.html">2. Securing Your Network</a></span></dt><dd><dl><dt><span class="section"><a href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security">2.1. Workstation Security</a>
</span></dt><dd><dl><dt><span class="section"><a href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security-Evaluating_Workstation_Security">2.1.1. Evaluating Workstation Security</a></span></dt><dt><span class="section"><a href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security-BIOS_and_Boot_Loader_Security">2.1.2. BIOS and Boot Loader Security</a></span></dt><dt><span class="section"><a href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security-Password_Security">2.1.3. Password Security</a></span></dt><dt><span class="section"><a href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security-Administrative_Controls">2.1.4. Administrative Controls</a></span></dt><dt><span class="section"><a href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security-Available_Network_Services">2.1.5. Available Network S
ervices</a></span></dt><dt><span class="section"><a href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security-Personal_Firewalls">2.1.6. Personal Firewalls</a></span></dt><dt><span class="section"><a href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security-Security_Enhanced_Communication_Tools">2.1.7. Security Enhanced Communication Tools</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Server_Security.html">2.2. Server Security</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Server_Security.html#sect-Security_Guide-Server_Security-Securing_Services_With_TCP_Wrappers_and_xinetd">2.2.1. Securing Services With TCP Wrappers and xinetd</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Server_Security-Securing_Portmap.html">2.2.2. Securing Portmap</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Server_Secur
ity-Securing_NIS.html">2.2.3. Securing NIS</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Server_Security-Securing_NFS.html">2.2.4. Securing NFS</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Server_Security-Securing_the_Apache_HTTP_Server.html">2.2.5. Securing the Apache HTTP Server</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Server_Security-Securing_FTP.html">2.2.6. Securing FTP</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Server_Security-Securing_Sendmail.html">2.2.7. Securing Sendmail</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Server_Security-Verifying_Which_Ports_Are_Listening.html">2.2.8. Verifying Which Ports Are Listening</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Single_Sign_on_SSO.html">2.3. Single Sign-on (SSO)</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Single_Sign_on_SSO
.html#sect-Security_Guide-Single_Sign_on_SSO-Introduction">2.3.1. Introduction</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Single_Sign_on_SSO-Getting_Started_with_your_new_Smart_Card.html">2.3.2. Getting Started with your new Smart Card</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Single_Sign_on_SSO-How_Smart_Card_Enrollment_Works.html">2.3.3. How Smart Card Enrollment Works</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Single_Sign_on_SSO-How_Smart_Card_Login_Works.html">2.3.4. How Smart Card Login Works</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Single_Sign_on_SSO-Configuring_Firefox_to_use_Kerberos_for_SSO.html">2.3.5. Configuring Firefox to use Kerberos for SSO</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM.html">2.4. Pluggable Authentication Modules (PAM)</a></span></dt><dd><dl><dt><span class="section
"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM.html#sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Advantages_of_PAM">2.4.1. Advantages of PAM</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_Configuration_Files.html">2.4.2. PAM Configuration Files</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_Configuration_File_Format.html">2.4.3. PAM Configuration File Format</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Sample_PAM_Configuration_Files.html">2.4.4. Sample PAM Configuration Files</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Creating_PAM_Modules.html">2.4.5. Creating PAM Modules</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Administ
rative_Credential_Caching.html">2.4.6. PAM and Administrative Credential Caching</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Device_Ownership.html">2.4.7. PAM and Device Ownership</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Additional_Resources.html">2.4.8. Additional Resources</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-TCP_Wrappers_and_xinetd.html">2.5. TCP Wrappers and xinetd</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-TCP_Wrappers_and_xinetd.html#sect-Security_Guide-TCP_Wrappers_and_xinetd-TCP_Wrappers">2.5.1. TCP Wrappers</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-TCP_Wrappers_and_xinetd-TCP_Wrappers_Configuration_Files.html">2.5.2. TCP Wrappers Configuration Files</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-TCP_Wrapp
ers_and_xinetd-xinetd.html">2.5.3. xinetd</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-TCP_Wrappers_and_xinetd-xinetd_Configuration_Files.html">2.5.4. xinetd Configuration Files</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-TCP_Wrappers_and_xinetd-Additional_Resources.html">2.5.5. Additional Resources</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Kerberos.html">2.6. Kerberos</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Kerberos.html#sect-Security_Guide-Kerberos-What_is_Kerberos">2.6.1. What is Kerberos?</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-Kerberos_Terminology.html">2.6.2. Kerberos Terminology</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-How_Kerberos_Works.html">2.6.3. How Kerberos Works</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-Kerberos_and_PAM.html
">2.6.4. Kerberos and PAM</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Server.html">2.6.5. Configuring a Kerberos 5 Server</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Client.html">2.6.6. Configuring a Kerberos 5 Client</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-Domain_to_Realm_Mapping.html">2.6.7. Domain-to-Realm Mapping</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-Setting_Up_Secondary_KDCs.html">2.6.8. Setting Up Secondary KDCs</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-Setting_Up_Cross_Realm_Authentication.html">2.6.9. Setting Up Cross Realm Authentication</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Kerberos-Additional_Resources.html">2.6.10. Additional Resources</a></span></dt></dl></dd><dt><span class="section"><a href="sect
-Security_Guide-Virtual_Private_Networks_VPNs.html">2.7. Virtual Private Networks (VPNs)</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPNs.html#sect-Security_Guide-Virtual_Private_Networks_VPNs-How_Does_a_VPN_Work">2.7.1. How Does a VPN Work?</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPNs-VPNs_and_PROD.html">2.7.2. VPNs and Fedora</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec.html">2.7.3. IPsec</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPNs-Creating_an_IPsec_Connection.html">2.7.4. Creating an IPsec Connection</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec_Installation.html">2.7.5. IPsec Installation</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPN
s-IPsec_Host_to_Host_Configuration.html">2.7.6. IPsec Host-to-Host Configuration</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec_Network_to_Network_Configuration.html">2.7.7. IPsec Network-to-Network Configuration</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Virtual_Private_Networks_VPNs-Starting_and_Stopping_an_IPsec_Connection.html">2.7.8. Starting and Stopping an IPsec Connection</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Firewalls.html">2.8. Firewalls</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Firewalls.html#sect-Security_Guide-Firewalls-Netfilter_and_IPTables">2.8.1. Netfilter and IPTables</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Firewalls-Basic_Firewall_Configuration.html">2.8.2. Basic Firewall Configuration</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Firewalls-U
sing_IPTables.html">2.8.3. Using IPTables</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Firewalls-Common_IPTables_Filtering.html">2.8.4. Common IPTables Filtering</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Firewalls-FORWARD_and_NAT_Rules.html">2.8.5. FORWARD and NAT Rules</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Firewalls-Malicious_Software_and_Spoofed_IP_Addresses.html">2.8.6. Malicious Software and Spoofed IP Addresses</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Firewalls-IPTables_and_Connection_Tracking.html">2.8.7. IPTables and Connection Tracking</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Firewalls-IPv6.html">2.8.8. IPv6</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Firewalls-Additional_Resources.html">2.8.9. Additional Resources</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-IPTable
s.html">2.9. IPTables</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-IPTables.html#sect-Security_Guide-IPTables-Packet_Filtering">2.9.1. Packet Filtering</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-IPTables-Differences_Between_IPTables_and_IPChains.html">2.9.2. Differences Between IPTables and IPChains</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-IPTables-Command_Options_for_IPTables.html">2.9.3. Command Options for IPTables</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-IPTables-Saving_IPTables_Rules.html">2.9.4. Saving IPTables Rules</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-IPTables-IPTables_Control_Scripts.html">2.9.5. IPTables Control Scripts</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-IPTables-IPTables_and_IPv6.html">2.9.6. IPTables and IPv6</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-IP
Tables-Additional_Resources.html">2.9.7. Additional Resources</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="chap-Security_Guide-Encryption.html">3. Encryption</a></span></dt><dd><dl><dt><span class="section"><a href="chap-Security_Guide-Encryption.html#sect-Security_Guide-Encryption-Data_at_Rest">3.1. Data at Rest</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Encryption-Protecting_Data_at_Rest-Full_Disk_Encryption.html">3.2. Full Disk Encryption</a></span></dt><dt><span class="section"><a href="Security_Guide-Encryption-Protecting_Data_at_Rest-File_Based_Encryption.html">3.3. File Based Encryption</a></span></dt><dt><span class="section"><a href="Security_Guide-Encryption-Data_in_Motion.html">3.4. Data in Motion</a></span></dt><dt><span class="section"><a href="Security_Guide-Encryption-Data_in_Motion-Virtual_Private_Networks.html">3.5. Virtual Private Networks</a></span></dt><dt><span class="section"><a href="Security_Guide-En
cryption-Data_in_Motion-Secure_Shell.html">3.6. Secure Shell</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-LUKS_Disk_Encryption.html">3.7. LUKS Disk Encryption</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-LUKS_Disk_Encryption.html#sect-Security_Guide-LUKS_Disk_Encryption-LUKS_Implementation_in_Fedora">3.7.1. LUKS Implementation in Fedora</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories.html">3.7.2. Manually Encrypting Directories</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-Step_by_Step_Instructions.html">3.7.3. Step-by-Step Instructions</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-What_you_have_just_accomplished.html">3.7.4. What you have just accomplished.</a></span></dt><dt><span class="sec
tion"><a href="sect-Security_Guide-LUKS_Disk_Encryption-Links_of_Interest.html">3.7.5. Links of Interest</a></span></dt></dl></dd><dt><span class="section"><a href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives.html">3.8. 7-Zip Encrypted Archives</a></span></dt><dd><dl><dt><span class="section"><a href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives.html#sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Installation">3.8.1. 7-Zip Installation in Fedora</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Installation-Instructions.html">3.8.2. Step-by-Step Installation Instructions</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Usage_Instructions.html">3.8.3. Step-by-Step Usage Instructions</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Things_of_note.html">3.8.4. Things of note</a><
/span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="chap-Security_Guide-General_Principles_of_Information_Security.html">4. General Principles of Information Security</a></span></dt><dd><dl><dt><span class="section"><a href="chap-Security_Guide-General_Principles_of_Information_Security.html#sect-Security_Guide-General_Principles_of_Information_Security-General_Principles">4.1. General Principles</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-General_Principles_of_Information_Security-Tips_Guides_and_Tools.html">4.2. Tips, Guides, and Tools</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-General_Principles_of_Information_Security-NSA_Documents.html">4.3. NSA Documents</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-General_Principles_of_Information_Security-DISA_IASE_Documents.html">4.4. DISA IASE Documents</a></span></dt></dl></dd><dt><span class="chapter"><a href="chap-Security_Guide-Secure_In
stallation.html">5. Secure Installation</a></span></dt><dd><dl><dt><span class="section"><a href="chap-Security_Guide-Secure_Installation.html#sect-Security_Guide-Secure_Installation-Disk_Partitions">5.1. Disk Partitions</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Secure_Installation-Utilize_LUKS_Partition_Encryption.html">5.2. Utilize LUKS Partition Encryption</a></span></dt></dl></dd><dt><span class="chapter"><a href="chap-Security_Guide-Software_Maintenance.html">6. Software Maintenance</a></span></dt><dd><dl><dt><span class="section"><a href="chap-Security_Guide-Software_Maintenance.html#sect-Security_Guide-Software_Maintenance-Install_Minimal_Software">6.1. Install Minimal Software</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Software_Maintenance-Plan_and_Configure_Security_Updates.html">6.2. Plan and Configure Security Updates</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Software_Maintenance-Pl
an_and_Configure_Security_Updates-Adjusting_Automatic_Updates.html">6.3. Adjusting Automatic Updates</a></span></dt><dt><span class="section"><a href="sect-Security_Guide-Software_Maintenance-Install_Signed_Packages_from_Well_Known_Repositories.html">6.4. Install Signed Packages from Well Known Repositories</a></span></dt></dl></dd><dt><span class="chapter"><a href="chap-Security_Guide-References.html">7. References</a></span></dt></dl></div></div><ul class="docnav"><li class="previous"/><li class="next"><a accesskey="n" href="pref-Security_Guide-Preface.html"><strong>Next</strong>Preface</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Preface</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="index.html" title="Linux Security Guide"/><link rel="prev" href="index.html" title="Linux Security Guide"/><link rel="next" href="We_Need_Feedback.html" title="2. We Need Feedback!"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="index.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="We_Need_Feedback.h
tml"><strong>Next</strong></a></li></ul><div class="preface" lang="en-US"><div class="titlepage"><div><div><h1 id="pref-Security_Guide-Preface" class="title">Preface</h1></div></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="d0e91">1. Document Conventions</h2></div></div></div><div class="para">
This manual uses several conventions to highlight certain words and phrases and draw attention to specific pieces of information.
</div><div class="para">
In PDF and paper editions, this manual uses typefaces drawn from the <a href="https://fedorahosted.org/liberation-fonts/">Liberation Fonts</a> set. The Liberation Fonts set is also used in HTML editions if the set is installed on your system. If not, alternative but equivalent typefaces are displayed. Note: Red Hat Enterprise Linux 5 and later includes the Liberation Fonts set by default.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="d0e101">1.1. Typographic Conventions</h3></div></div></div><div class="para">
Four typographic conventions are used to call attention to specific words and phrases. These conventions, and the circumstances they apply to, are as follows.
</div><div class="para">
<code class="literal">Mono-spaced Bold</code>
</div><div class="para">
Used to highlight system input, including shell commands, file names and paths. Also used to highlight key caps and key-combinations. For example:
</div><div class="blockquote"><blockquote class="blockquote"><div class="para">
To see the contents of the file <code class="filename">my_next_bestselling_novel</code> in your current working directory, enter the <code class="command">cat my_next_bestselling_novel</code> command at the shell prompt and press <span class="keycap"><strong>Enter</strong></span> to execute the command.
</div></blockquote></div><div class="para">
The above includes a file name, a shell command and a key cap, all presented in Mono-spaced Bold and all distinguishable thanks to context.
</div><div class="para">
Key-combinations can be distinguished from key caps by the hyphen connecting each part of a key-combination. For example:
</div><div class="blockquote"><blockquote class="blockquote"><div class="para">
Press <span class="keycap"><strong>Enter</strong></span> to execute the command.
</div><div class="para">
Press <span class="keycap"><strong>Ctrl</strong></span>+<span class="keycap"><strong>Alt</strong></span>+<span class="keycap"><strong>F1</strong></span> to switch to the first virtual terminal. Press <span class="keycap"><strong>Ctrl</strong></span>+<span class="keycap"><strong>Alt</strong></span>+<span class="keycap"><strong>F7</strong></span> to return to your X-Windows session.
</div></blockquote></div><div class="para">
The first sentence highlights the particular key cap to press. The second highlights two sets of three key caps, each set pressed simultaneously.
</div><div class="para">
If source code is discussed, class names, methods, functions, variable names and returned values mentioned within a paragraph will be presented as above, in <code class="literal">Mono-spaced Bold</code>. For example:
</div><div class="blockquote"><blockquote class="blockquote"><div class="para">
File-related classes include <code class="classname">filesystem</code> for file systems, <code class="classname">file</code> for files, and <code class="classname">dir</code> for directories. Each class has its own associated set of permissions.
</div></blockquote></div><div class="para">
<span class="application"><strong>Proportional Bold</strong></span>
</div><div class="para">
This denotes words or phrases encountered on a system, including application names; dialogue box text; labelled buttons; check-box and radio button labels; menu titles and sub-menu titles. For example:
</div><div class="blockquote"><blockquote class="blockquote"><div class="para">
Choose <span class="guimenu"><strong>System > Preferences > Mouse</strong></span> from the main menu bar to launch <span class="application"><strong>Mouse Preferences</strong></span>. In the <span class="guilabel"><strong>Buttons</strong></span> tab, click the <span class="guilabel"><strong>Left-handed mouse</strong></span> check box and click <span class="guibutton"><strong>Close</strong></span> to switch the primary mouse button from the left to the right (making the mouse suitable for use in the left hand).
</div><div class="para">
To insert a special character into a <span class="application"><strong>gedit</strong></span> file, choose <span class="guimenu"><strong>Applications > Accessories > Character Map</strong></span> from the main menu bar. Next, choose <span class="guimenu"><strong>Search > Find…</strong></span> from the <span class="application"><strong>Character Map</strong></span> menu bar, type the name of the character in the <span class="guilabel"><strong>Search</strong></span> field and click <span class="guibutton"><strong>Next</strong></span>. The character you sought will be highlighted in the <span class="guilabel"><strong>Character Table</strong></span>. Double-click this highlighted character to place it in the <span class="guilabel"><strong>Text to copy</strong></span> field and then click the <span class="guibutton"><strong>Copy</strong></span> button. Now switch back to your document and choose <span class="guimenu"><strong>Edit > Paste</strong></span> from the <
span class="application"><strong>gedit</strong></span> menu bar.
</div></blockquote></div><div class="para">
The above text includes application names; system-wide menu names and items; application-specific menu names; and buttons and text found within a GUI interface, all presented in Proportional Bold and all distinguishable by context.
</div><div class="para">
Note the <span class="guimenu"><strong>></strong></span> shorthand used to indicate traversal through a menu and its sub-menus. This is to avoid the difficult-to-follow 'Select <span class="guimenuitem"><strong>Mouse</strong></span> from the <span class="guimenu"><strong>Preferences</strong></span> sub-menu in the <span class="guimenu"><strong>System</strong></span> menu of the main menu bar' approach.
</div><div class="para">
<code class="command"><em class="replaceable"><code>Mono-spaced Bold Italic</code></em></code> or <span class="application"><strong><em class="replaceable"><code>Proportional Bold Italic</code></em></strong></span>
</div><div class="para">
Whether Mono-spaced Bold or Proportional Bold, the addition of Italics indicates replaceable or variable text. Italics denotes text you do not input literally or displayed text that changes depending on circumstance. For example:
</div><div class="blockquote"><blockquote class="blockquote"><div class="para">
To connect to a remote machine using ssh, type <code class="command">ssh <em class="replaceable"><code>username</code></em>@<em class="replaceable"><code>domain.name</code></em></code> at a shell prompt. If the remote machine is <code class="filename">example.com</code> and your username on that machine is john, type <code class="command">ssh john(a)example.com</code>.
</div><div class="para">
The <code class="command">mount -o remount <em class="replaceable"><code>file-system</code></em></code> command remounts the named file system. For example, to remount the <code class="filename">/home</code> file system, the command is <code class="command">mount -o remount /home</code>.
</div><div class="para">
To see the version of a currently installed package, use the <code class="command">rpm -q <em class="replaceable"><code>package</code></em></code> command. It will return a result as follows: <code class="command"><em class="replaceable"><code>package-version-release</code></em></code>.
</div></blockquote></div><div class="para">
Note the words in bold italics above — username, domain.name, file-system, package, version and release. Each word is a placeholder, either for text you enter when issuing a command or for text displayed by the system.
</div><div class="para">
Aside from standard usage for presenting the title of a work, italics denotes the first use of a new and important term. For example:
</div><div class="blockquote"><blockquote class="blockquote"><div class="para">
When the Apache HTTP Server accepts requests, it dispatches child processes or threads to handle them. This group of child processes or threads is known as a <em class="firstterm">server-pool</em>. Under Apache HTTP Server 2.0, the responsibility for creating and maintaining these server-pools has been abstracted to a group of modules called <em class="firstterm">Multi-Processing Modules</em> (<em class="firstterm">MPMs</em>). Unlike other modules, only one module from the MPM group can be loaded by the Apache HTTP Server.
</div></blockquote></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="d0e317">1.2. Pull-quote Conventions</h3></div></div></div><div class="para">
Two, commonly multi-line, data types are set off visually from the surrounding text.
</div><div class="para">
Output sent to a terminal is set in <code class="computeroutput">Mono-spaced Roman</code> and presented thus:
</div><pre class="screen">
books Desktop documentation drafts mss photos stuff svn
books_tests Desktop1 downloads images notes scripts svgs
</pre><div class="para">
Source-code listings are also set in <code class="computeroutput">Mono-spaced Roman</code> but are presented and highlighted as follows:
</div><pre class="programlisting">
package org.jboss.book.jca.ex1;
import javax.naming.InitialContext;
public class ExClient
{
public static void main(String args[])
throws Exception
{
InitialContext iniCtx = new InitialContext();
Object ref = iniCtx.lookup("EchoBean");
EchoHome home = (EchoHome) ref;
Echo echo = home.create();
System.out.println("Created Echo");
System.out.println("Echo.echo('Hello') = " + echo.echo("Hello"));
}
}
</pre></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="d0e336">1.3. Notes and Warnings</h3></div></div></div><div class="para">
Finally, we use three visual styles to draw attention to information that might otherwise be overlooked.
</div><div class="note"><h2>Note</h2><div class="para">
A note is a tip or shortcut or alternative approach to the task at hand. Ignoring a note should have no negative consequences, but you might miss out on a trick that makes your life easier.
</div></div><div class="important"><h2>Important</h2><div class="para">
Important boxes detail things that are easily missed: configuration changes that only apply to the current session, or services that need restarting before an update will apply. Ignoring Important boxes won't cause data loss but may cause irritation and frustration.
</div></div><div class="warning"><h2>Warning</h2><div class="para">
A Warning should not be ignored. Ignoring warnings will most likely cause data loss.
</div></div></div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="index.html"><strong>Prev</strong>Linux Security Guide</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="We_Need_Feedback.html"><strong>Next</strong>2. We Need Feedback!</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.5.5.3. Related Books</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-TCP_Wrappers_and_xinetd-Additional_Resources.html" title="2.5.5. Additional Resources"/><link rel="prev" href="sect-Security_Guide-Additional_Resources-Useful_TCP_Wrappers_Websites.html" title="2.5.5.2. Useful TCP Wrappers Websites"/><link rel="next" href="sect-Security_Guide-Kerberos.html" title="2.6. Kerberos"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/><
/a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Additional_Resources-Useful_TCP_Wrappers_Websites.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Additional_Resources-Related_Books">2.5.5.3. Related Books</h4></div></div></div><a id="d0e9152" class="indexterm"/><a id="d0e9159" class="indexterm"/><div class="itemizedlist"><ul><li><div class="para">
<em class="citetitle">Hacking Linux Exposed</em> by Brian Hatch, James Lee, and George Kurtz; Osbourne/McGraw-Hill — An excellent security resource with information about TCP Wrappers and <code class="systemitem">xinetd</code>.
</div></li></ul></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Additional_Resources-Useful_TCP_Wrappers_Websites.html"><strong>Prev</strong>2.5.5.2. Useful TCP Wrappers Websites</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos.html"><strong>Next</strong>2.6. Kerberos</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.8.9.3. Related Documentation</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Firewalls-Additional_Resources.html" title="2.8.9. Additional Resources"/><link rel="prev" href="sect-Security_Guide-Additional_Resources-Useful_Firewall_Websites.html" title="2.8.9.2. Useful Firewall Websites"/><link rel="next" href="sect-Security_Guide-IPTables.html" title="2.9. IPTables"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul cla
ss="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Additional_Resources-Useful_Firewall_Websites.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Additional_Resources-Related_Documentation">2.8.9.3. Related Documentation</h4></div></div></div><div class="itemizedlist"><ul><li><div class="para">
<em class="citetitle">Red Hat Linux Firewalls</em>, by Bill McCarty; Red Hat Press — a comprehensive reference to building network and server firewalls using open source packet filtering technology such as Netfilter and <code class="command">iptables</code>. It includes topics that cover analyzing firewall logs, developing firewall rules, and customizing your firewall using various graphical tools.
</div></li><li><div class="para">
<em class="citetitle">Linux Firewalls</em>, by Robert Ziegler; New Riders Press — contains a wealth of information on building firewalls using both 2.2 kernel <code class="command">ipchains</code> as well as Netfilter and <code class="command">iptables</code>. Additional security topics such as remote access issues and intrusion detection systems are also covered.
</div></li></ul></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Additional_Resources-Useful_Firewall_Websites.html"><strong>Prev</strong>2.8.9.2. Useful Firewall Websites</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables.html"><strong>Next</strong>2.9. IPTables</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.8.9.2. Useful Firewall Websites</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Firewalls-Additional_Resources.html" title="2.8.9. Additional Resources"/><link rel="prev" href="sect-Security_Guide-Firewalls-Additional_Resources.html" title="2.8.9. Additional Resources"/><link rel="next" href="sect-Security_Guide-Additional_Resources-Related_Documentation.html" title="2.8.9.3. Related Documentation"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Doc
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<a href="http://www.netfilter.org/">http://www.netfilter.org/</a> — The official homepage of the Netfilter and <code class="command">iptables</code> project.
</div></li><li><div class="para">
<a href="http://www.tldp.org/">http://www.tldp.org/</a> — The Linux Documentation Project contains several useful guides relating to firewall creation and administration.
</div></li><li><div class="para">
<a href="http://www.iana.org/assignments/port-numbers">http://www.iana.org/assignments/port-numbers</a> — The official list of registered and common service ports as assigned by the Internet Assigned Numbers Authority.
</div></li></ul></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Firewalls-Additional_Resources.html"><strong>Prev</strong>2.8.9. Additional Resources</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Additional_Resources-Related_Documentation.html"><strong>Next</strong>2.8.9.3. Related Documentation</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.9.7.2. Useful IP Tables Websites</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-IPTables-Additional_Resources.html" title="2.9.7. Additional Resources"/><link rel="prev" href="sect-Security_Guide-IPTables-Additional_Resources.html" title="2.9.7. Additional Resources"/><link rel="next" href="chap-Security_Guide-Encryption.html" title="Chapter 3. Encryption"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docn
av"><li class="previous"><a accesskey="p" href="sect-Security_Guide-IPTables-Additional_Resources.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="chap-Security_Guide-Encryption.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Additional_Resources-Useful_IP_Tables_Websites">2.9.7.2. Useful IP Tables Websites</h4></div></div></div><a id="d0e16278" class="indexterm"/><div class="itemizedlist"><ul><li><div class="para">
<a href="http://www.netfilter.org/">http://www.netfilter.org/</a> — The home of the netfilter/iptables project. Contains assorted information about <code class="command">iptables</code>, including a FAQ addressing specific problems and various helpful guides by Rusty Russell, the Linux IP firewall maintainer. The HOWTO documents on the site cover subjects such as basic networking concepts, kernel packet filtering, and NAT configurations.
</div></li><li><div class="para">
<a href="http://www.linuxnewbie.org/nhf/Security/IPtables_Basics.html">http://www.linuxnewbie.org/nhf/Security/IPtables_Basics.html</a> — An introduction to the way packets move through the Linux kernel, plus an introduction to constructing basic <code class="command">iptables</code> commands.
</div></li></ul></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-IPTables-Additional_Resources.html"><strong>Prev</strong>2.9.7. Additional Resources</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="chap-Security_Guide-Encryption.html"><strong>Next</strong>Chapter 3. Encryption</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.6.10.2. Useful Kerberos Websites</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Kerberos-Additional_Resources.html" title="2.6.10. Additional Resources"/><link rel="prev" href="sect-Security_Guide-Kerberos-Additional_Resources.html" title="2.6.10. Additional Resources"/><link rel="next" href="sect-Security_Guide-Virtual_Private_Networks_VPNs.html" title="2.7. Virtual Private Networks (VPNs)"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documenta
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<a href="http://web.mit.edu/kerberos/www/">http://web.mit.edu/kerberos/www/</a> — <em class="citetitle">Kerberos: The Network Authentication Protocol</em> webpage from MIT.
</div></li><li><div class="para">
<a href="http://www.nrl.navy.mil/CCS/people/kenh/kerberos-faq.html">http://www.nrl.navy.mil/CCS/people/kenh/kerberos-faq.html</a> — The Kerberos Frequently Asked Questions (FAQ).
</div></li><li><div class="para">
<a href="ftp://athena-dist.mit.edu/pub/kerberos/doc/usenix.PS">ftp://athena-dist.mit.edu/pub/kerberos/doc/usenix.PS</a> — The PostScript version of <em class="citetitle">Kerberos: An Authentication Service for Open Network Systems</em> by Jennifer G. Steiner, Clifford Neuman, and Jeffrey I. Schiller. This document is the original paper describing Kerberos.
</div></li><li><div class="para">
<a href="http://web.mit.edu/kerberos/www/dialogue.html">http://web.mit.edu/kerberos/www/dialogue.html</a> — <em class="citetitle">Designing an Authentication System: a Dialogue in Four Scenes</em> originally by Bill Bryant in 1988, modified by Theodore Ts'o in 1997. This document is a conversation between two developers who are thinking through the creation of a Kerberos-style authentication system. The conversational style of the discussion make this a good starting place for people who are completely unfamiliar with Kerberos.
</div></li><li><div class="para">
<a href="http://www.ornl.gov/~jar/HowToKerb.html">http://www.ornl.gov/~jar/HowToKerb.html</a> — <em class="citetitle">How to Kerberize your site</em> is a good reference for kerberizing a network.
</div></li><li><div class="para">
<a href="http://www.networkcomputing.com/netdesign/kerb1.html">http://www.networkcomputing.com/netdesign/kerb1.html</a> — <em class="citetitle">Kerberos Network Design Manual</em> is a thorough overview of the Kerberos system.
</div></li></ul></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Kerberos-Additional_Resources.html"><strong>Prev</strong>2.6.10. Additional Resources</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Virtual_Private_Networks_VPNs.html"><strong>Next</strong>2.7. Virtual Private Networks (VPNs)</a></li></ul></body></html>
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<a href="http://www.kernel.org/pub/linux/libs/pam/">http://www.kernel.org/pub/linux/libs/pam/</a> — The primary distribution website for the Linux-PAM project, containing information on various PAM modules, a FAQ, and additional PAM documentation.
</div><div class="note"><h2>Note</h2><div class="para">
The documentation in the above website is for the last released upstream version of PAM and might not be 100% accurate for the PAM version included in Fedora.
</div></div></li></ul></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Additional_Resources.html"><strong>Prev</strong>2.4.8. Additional Resources</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-TCP_Wrappers_and_xinetd.html"><strong>Next</strong>2.5. TCP Wrappers and xinetd</a></li></ul></body></html>
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<a href="http://www.xinetd.org">http://www.xinetd.org/</a> — The home of <code class="systemitem">xinetd</code>, containing sample configuration files, a full listing of features, and an informative FAQ.
</div></li><li><div class="para">
<a href="http://www.macsecurity.org/resources/xinetd/tutorial.shtml">http://www.macsecurity.org/resources/xinetd/tutorial.shtml</a> — A thorough tutorial that discusses many different ways to optimize default <code class="systemitem">xinetd</code> configuration files to meet specific security goals.
</div></li></ul></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-TCP_Wrappers_and_xinetd-Additional_Resources.html"><strong>Prev</strong>2.5.5. Additional Resources</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Additional_Resources-Related_Books.html"><strong>Next</strong>2.5.5.3. Related Books</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.5.4.3.2. Access Control Options</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-xinetd_Configuration_Files-Altering_xinetd_Configuration_Files.html" title="2.5.4.3. Altering xinetd Configuration Files"/><link rel="prev" href="sect-Security_Guide-xinetd_Configuration_Files-Altering_xinetd_Configuration_Files.html" title="2.5.4.3. Altering xinetd Configuration Files"/><link rel="next" href="sect-Security_Guide-Altering_xinetd_Configuration_Files-Binding_and_Redirection_Options.html" title="2.5.4.3.3. Binding and Redirection Options"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png"
alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-xinetd_Configuration_Files-Altering_xinetd_Configuration_Files.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Altering_xinetd_Configuration_Files-Binding_and_Redirection_Options.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Altering_xinetd_Configuration_Files-Access_Control_Options">2.5.4.3.2. Access Control Options</h5></div></div></div><a id="d0e8648" class="indexterm"/><a id="d0e8656" class="indexterm"/><div class="para">
Users of <code class="systemitem">xinetd</code> services can choose to use the TCP Wrappers hosts access rules, provide access control via the <code class="systemitem">xinetd</code> configuration files, or a mixture of both. Refer to <a class="xref" href="sect-Security_Guide-TCP_Wrappers_and_xinetd-TCP_Wrappers_Configuration_Files.html" title="2.5.2. TCP Wrappers Configuration Files">Section 2.5.2, “TCP Wrappers Configuration Files”</a> for more information about TCP Wrappers hosts access control files.
</div><div class="para">
This section discusses using <code class="systemitem">xinetd</code> to control access to services.
</div><div class="note"><h2>Note</h2><div class="para">
Unlike TCP Wrappers, changes to access control only take effect if the <code class="systemitem">xinetd</code> administrator restarts the <code class="systemitem">xinetd</code> service.
</div><div class="para">
Also, unlike TCP Wrappers, access control through <code class="systemitem">xinetd</code> only affects services controlled by <code class="systemitem">xinetd</code>.
</div></div><div class="para">
The <code class="systemitem">xinetd</code> hosts access control differs from the method used by TCP Wrappers. While TCP Wrappers places all of the access configuration within two files, <code class="filename">/etc/hosts.allow</code> and <code class="filename">/etc/hosts.deny</code>, <code class="systemitem">xinetd</code>'s access control is found in each service's configuration file in the <code class="filename">/etc/xinetd.d/</code> directory.
</div><div class="para">
The following hosts access options are supported by <code class="systemitem">xinetd</code>:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">only_from</code> — Allows only the specified hosts to use the service.
</div></li><li><div class="para">
<code class="option">no_access</code> — Blocks listed hosts from using the service.
</div></li><li><div class="para">
<code class="option">access_times</code> — Specifies the time range when a particular service may be used. The time range must be stated in 24-hour format notation, HH:MM-HH:MM.
</div></li></ul></div><div class="para">
The <code class="option">only_from</code> and <code class="option">no_access</code> options can use a list of IP addresses or host names, or can specify an entire network. Like TCP Wrappers, combining <code class="systemitem">xinetd</code> access control with the enhanced logging configuration can increase security by blocking requests from banned hosts while verbosely recording each connection attempt.
</div><div class="para">
For example, the following <code class="filename">/etc/xinetd.d/telnet</code> file can be used to block Telnet access from a particular network group and restrict the overall time range that even allowed users can log in:
</div><pre class="screen">service telnet
{
disable = no
flags = REUSE
socket_type = stream
wait = no
user = root
server = /usr/kerberos/sbin/telnetd
log_on_failure += USERID
no_access = 172.16.45.0/24
log_on_success += PID HOST EXIT
access_times = 09:45-16:15
}
</pre><div class="para">
In this example, when a client system from the <code class="systemitem">10.0.1.0/24</code> network, such as <code class="systemitem">10.0.1.2</code>, tries to access the Telnet service, it receives the following message:
</div><pre class="screen">Connection closed by foreign host.
</pre><div class="para">
In addition, their login attempts are logged in <code class="filename">/var/log/messages</code> as follows:
</div><pre class="screen">Sep 7 14:58:33 localhost xinetd[5285]: FAIL: telnet address from=172.16.45.107
Sep 7 14:58:33 localhost xinetd[5283]: START: telnet pid=5285 from=172.16.45.107
Sep 7 14:58:33 localhost xinetd[5283]: EXIT: telnet status=0 pid=5285 duration=0(sec)
</pre><div class="para">
When using TCP Wrappers in conjunction with <code class="systemitem">xinetd</code> access controls, it is important to understand the relationship between the two access control mechanisms.
</div><div class="para">
The following is the sequence of events followed by <code class="systemitem">xinetd</code> when a client requests a connection:
</div><div class="orderedlist"><ol><li><div class="para">
The <code class="systemitem">xinetd</code> daemon accesses the TCP Wrappers hosts access rules using a <code class="filename">libwrap.a</code> library call. If a deny rule matches the client, the connection is dropped. If an allow rule matches the client, the connection is passed to <code class="systemitem">xinetd</code>.
</div></li><li><div class="para">
The <code class="systemitem">xinetd</code> daemon checks its own access control rules both for the <code class="systemitem">xinetd</code> service and the requested service. If a deny rule matches the client, the connection is dropped. Otherwise, <code class="systemitem">xinetd</code> starts an instance of the requested service and passes control of the connection to that service.
</div></li></ol></div><div class="important"><h2>Important</h2><div class="para">
Care should be taken when using TCP Wrappers access controls in conjunction with <code class="systemitem">xinetd</code> access controls. Misconfiguration can cause undesirable effects.
</div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-xinetd_Configuration_Files-Altering_xinetd_Configuration_Files.html"><strong>Prev</strong>2.5.4.3. Altering xinetd Configuration Files</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Altering_xinetd_Configuration_Files-Binding_and_Redirection_Options.html"><strong>Next</strong>2.5.4.3.3. Binding and Redirection Options</a></li></ul></body></html>
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ite"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Altering_xinetd_Configuration_Files-Access_Control_Options.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Altering_xinetd_Configuration_Files-Resource_Management_Options.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Altering_xinetd_Configuration_Files-Binding_and_Redirection_Options">2.5.4.3.3. Binding and Redirection Options</h5></div></div></div><a id="d0e8818" class="indexterm"/><a id="d0e8826" class="indexterm"/><div class="para">
The service configuration files for <code class="systemitem">xinetd</code> support binding the service to an IP address and redirecting incoming requests for that service to another IP address, hostname, or port.
</div><div class="para">
Binding is controlled with the <code class="option">bind</code> option in the service-specific configuration files and links the service to one IP address on the system. When this is configured, the <code class="option">bind</code> option only allows requests to the correct IP address to access the service. You can use this method to bind different services to different network interfaces based on requirements.
</div><div class="para">
This is particularly useful for systems with multiple network adapters or with multiple IP addresses. On such a system, insecure services (for example, Telnet), can be configured to listen only on the interface connected to a private network and not to the interface connected to the Internet.
</div><div class="para">
The <code class="option">redirect</code> option accepts an IP address or hostname followed by a port number. It configures the service to redirect any requests for this service to the specified host and port number. This feature can be used to point to another port number on the same system, redirect the request to a different IP address on the same machine, shift the request to a totally different system and port number, or any combination of these options. A user connecting to a certain service on a system may therefore be rerouted to another system without disruption.
</div><div class="para">
The <code class="systemitem">xinetd</code> daemon is able to accomplish this redirection by spawning a process that stays alive for the duration of the connection between the requesting client machine and the host actually providing the service, transferring data between the two systems.
</div><div class="para">
The advantages of the <code class="option">bind</code> and <code class="option">redirect</code> options are most clearly evident when they are used together. By binding a service to a particular IP address on a system and then redirecting requests for this service to a second machine that only the first machine can see, an internal system can be used to provide services for a totally different network. Alternatively, these options can be used to limit the exposure of a particular service on a multi-homed machine to a known IP address, as well as redirect any requests for that service to another machine especially configured for that purpose.
</div><div class="para">
For example, consider a system that is used as a firewall with this setting for its Telnet service:
</div><pre class="screen">service telnet
{
socket_type = stream
wait = no
server = /usr/kerberos/sbin/telnetd
log_on_success += DURATION USERID
log_on_failure += USERID
bind = 123.123.123.123
redirect = 10.0.1.13 23
}
</pre><div class="para">
The <code class="option">bind</code> and <code class="option">redirect</code> options in this file ensure that the Telnet service on the machine is bound to the external IP address (<code class="systemitem">123.123.123.123</code>), the one facing the Internet. In addition, any requests for Telnet service sent to <code class="systemitem">123.123.123.123</code> are redirected via a second network adapter to an internal IP address (<code class="systemitem">10.0.1.13</code>) that only the firewall and internal systems can access. The firewall then sends the communication between the two systems, and the connecting system thinks it is connected to <code class="systemitem">123.123.123.123</code> when it is actually connected to a different machine.
</div><div class="para">
This feature is particularly useful for users with broadband connections and only one fixed IP address. When using Network Address Translation (NAT), the systems behind the gateway machine, which are using internal-only IP addresses, are not available from outside the gateway system. However, when certain services controlled by <code class="systemitem">xinetd</code> are configured with the <code class="option">bind</code> and <code class="option">redirect</code> options, the gateway machine can act as a proxy between outside systems and a particular internal machine configured to provide the service. In addition, the various <code class="systemitem">xinetd</code> access control and logging options are also available for additional protection.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Altering_xinetd_Configuration_Files-Access_Control_Options.html"><strong>Prev</strong>2.5.4.3.2. Access Control Options</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Altering_xinetd_Configuration_Files-Resource_Management_Options.html"><strong>Next</strong>2.5.4.3.4. Resource Management Options</a></li></ul></body></html>
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ss="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Altering_xinetd_Configuration_Files-Binding_and_Redirection_Options.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-TCP_Wrappers_and_xinetd-Additional_Resources.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Altering_xinetd_Configuration_Files-Resource_Management_Options">2.5.4.3.4. Resource Management Options</h5></div></div></div><a id="d0e8908" class="indexterm"/><a id="d0e8916" class="indexterm"/><a id="d0e8922" class="indexterm"/><a id="d0e8927" class="indexterm"/><div class="para">
The <code class="systemitem">xinetd</code> daemon can add a basic level of protection from Denial of Service (DoS) attacks. The following is a list of directives which can aid in limiting the effectiveness of such attacks:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">per_source</code> — Defines the maximum number of instances for a service per source IP address. It accepts only integers as an argument and can be used in both <code class="filename">xinetd.conf</code> and in the service-specific configuration files in the <code class="filename">xinetd.d/</code> directory.
</div></li><li><div class="para">
<code class="option">cps</code> — Defines the maximum number of connections per second. This directive takes two integer arguments separated by white space. The first argument is the maximum number of connections allowed to the service per second. The second argument is the number of seconds that <code class="systemitem">xinetd</code> must wait before re-enabling the service. It accepts only integers as arguments and can be used in either the <code class="filename">xinetd.conf</code> file or the service-specific configuration files in the <code class="filename">xinetd.d/</code> directory.
</div></li><li><div class="para">
<code class="option">max_load</code> — Defines the CPU usage or load average threshold for a service. It accepts a floating point number argument.
</div><div class="para">
The load average is a rough measure of how many processes are active at a given time. See the <code class="command">uptime</code>, <code class="command">who</code>, and <code class="command">procinfo</code> commands for more information about load average.
</div></li></ul></div><div class="para">
There are more resource management options available for <code class="systemitem">xinetd</code>. Refer to the <code class="filename">xinetd.conf</code> man page for more information.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Altering_xinetd_Configuration_Files-Binding_and_Redirection_Options.html"><strong>Prev</strong>2.5.4.3.3. Binding and Redirection Options</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-TCP_Wrappers_and_xinetd-Additional_Resources.html"><strong>Next</strong>2.5.5. Additional Resources</a></li></ul></body></html>
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ages/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Attackers_and_Vulnerabilities.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Server_Security.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Network_Security">1.3.2. Threats to Network Security</h3></div></div></div><a id="d0e1033" class="indexterm"/><div class="para">
Bad practices when configuring the following aspects of a network can increase the risk of attack.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Threats_to_Network_Security-Insecure_Architectures">1.3.2.1. Insecure Architectures</h4></div></div></div><a id="d0e1043" class="indexterm"/><div class="para">
A misconfigured network is a primary entry point for unauthorized users. Leaving a trust-based, open local network vulnerable to the highly-insecure Internet is much like leaving a door ajar in a crime-ridden neighborhood — nothing may happen for an arbitrary amount of time, but <span class="emphasis"><em>eventually</em></span> someone exploits the opportunity.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Insecure_Architectures-Broadcast_Networks">1.3.2.1.1. Broadcast Networks</h5></div></div></div><div class="para">
System administrators often fail to realize the importance of networking hardware in their security schemes. Simple hardware such as hubs and routers rely on the broadcast or non-switched principle; that is, whenever a node transmits data across the network to a recipient node, the hub or router sends a broadcast of the data packets until the recipient node receives and processes the data. This method is the most vulnerable to address resolution protocol (<em class="firstterm">arp</em>) or media access control (<em class="firstterm">MAC</em>) address spoofing by both outside intruders and unauthorized users on local hosts.
</div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Insecure_Architectures-Centralized_Servers">1.3.2.1.2. Centralized Servers</h5></div></div></div><div class="para">
Another potential networking pitfall is the use of centralized computing. A common cost-cutting measure for many businesses is to consolidate all services to a single powerful machine. This can be convenient as it is easier to manage and costs considerably less than multiple-server configurations. However, a centralized server introduces a single point of failure on the network. If the central server is compromised, it may render the network completely useless or worse, prone to data manipulation or theft. In these situations, a central server becomes an open door which allows access to the entire network.
</div></div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Attackers_and_Vulnerabilities.html"><strong>Prev</strong>1.3. Attackers and Vulnerabilities</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Server_Security.html"><strong>Next</strong>1.3.3. Threats to Server Security</a></li></ul></body></html>
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Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Network_Security.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Threats_to_Server_Security-Unpatched_Services.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Server_Security">1.3.3. Threats to Server Security</h3></div></div></div><a id="d0e1074" class="indexterm"/><div class="para">
Server security is as important as network security because servers often hold a great deal of an organization's vital information. If a server is compromised, all of its contents may become available for the cracker to steal or manipulate at will. The following sections detail some of the main issues.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Threats_to_Server_Security-Unused_Services_and_Open_Ports">1.3.3.1. Unused Services and Open Ports</h4></div></div></div><a id="d0e1084" class="indexterm"/><div class="para">
A full installation of Fedora contains 1000+ application and library packages. However, most server administrators do not opt to install every single package in the distribution, preferring instead to install a base installation of packages, including several server applications.
</div><div class="para">
A common occurrence among system administrators is to install the operating system without paying attention to what programs are actually being installed. This can be problematic because unneeded services may be installed, configured with the default settings, and possibly turned on. This can cause unwanted services, such as Telnet, DHCP, or DNS, to run on a server or workstation without the administrator realizing it, which in turn can cause unwanted traffic to the server, or even, a potential pathway into the system for crackers. Refer To <a class="xref" href="sect-Security_Guide-Server_Security.html" title="2.2. Server Security">Section 2.2, “Server Security”</a> for information on closing ports and disabling unused services.
</div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Network_Security.html"><strong>Prev</strong>1.3.2. Threats to Network Security</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Threats_to_Server_Security-Unpatched_Services.html"><strong>Next</strong>1.3.3.2. Unpatched Services</a></li></ul></body></html>
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ght" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Threats_to_Server_Security-Inherently_Insecure_Services.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Threats_to_Workstation_and_Home_PC_Security-Vulnerable_Client_Applications.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Workstation_and_Home_PC_Security">1.3.4. Threats to Workstation and Home PC Security</h3></div></div></div><a id="d0e1172" class="indexterm"/><div class="para">
Workstations and home PCs may not be as prone to attack as networks or servers, but since they often contain sensitive data, such as credit card information, they are targeted by system crackers. Workstations can also be co-opted without the user's knowledge and used by attackers as "slave" machines in coordinated attacks. For these reasons, knowing the vulnerabilities of a workstation can save users the headache of reinstalling the operating system, or worse, recovering from data theft.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Threats_to_Workstation_and_Home_PC_Security-Bad_Passwords">1.3.4.1. Bad Passwords</h4></div></div></div><a id="d0e1182" class="indexterm"/><div class="para">
Bad passwords are one of the easiest ways for an attacker to gain access to a system. For more on how to avoid common pitfalls when creating a password, refer to <a class="xref" href="chap-Security_Guide-Securing_Your_Network.html#sect-Security_Guide-Workstation_Security-Password_Security" title="2.1.3. Password Security">Section 2.1.3, “Password Security”</a>.
</div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Threats_to_Server_Security-Inherently_Insecure_Services.html"><strong>Prev</strong>1.3.3.4. Inherently Insecure Services</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Threats_to_Workstation_and_Home_PC_Security-Vulnerable_Client_Applications.html"><strong>Next</strong>1.3.4.2. Vulnerable Client Applications</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>1.3. Attackers and Vulnerabilities</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="chap-Security_Guide-Security_Overview.html" title="Chapter 1. Security Overview"/><link rel="prev" href="sect-Security_Guide-Evaluating_the_Tools-Anticipating_Your_Future_Needs.html" title="1.2.3.5. Anticipating Your Future Needs"/><link rel="next" href="sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Network_Security.html" title="1.3.2. Threats to Network Security"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Commo
n_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Evaluating_the_Tools-Anticipating_Your_Future_Needs.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Network_Security.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-Attackers_and_Vulnerabilities">1.3. Attackers and Vulnerabilities</h2></div></div></div><a id="d0e933" class="indexterm"/><div class="para">
To plan and implement a good security strategy, first be aware of some of the issues which determined, motivated attackers exploit to compromise systems. But before detailing these issues, the terminology used when identifying an attacker must be defined.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Attackers_and_Vulnerabilities-A_Quick_History_of_Hackers">1.3.1. A Quick History of Hackers</h3></div></div></div><a id="d0e941" class="indexterm"/><a id="d0e946" class="indexterm"/><div class="para">
The modern meaning of the term <em class="firstterm">hacker</em> has origins dating back to the 1960s and the Massachusetts Institute of Technology (MIT) Tech Model Railroad Club, which designed train sets of large scale and intricate detail. Hacker was a name used for club members who discovered a clever trick or workaround for a problem.
</div><div class="para">
The term hacker has since come to describe everything from computer buffs to gifted programmers. A common trait among most hackers is a willingness to explore in detail how computer systems and networks function with little or no outside motivation. Open source software developers often consider themselves and their colleagues to be hackers, and use the word as a term of respect.
</div><a id="d0e958" class="indexterm"/><div class="para">
Typically, hackers follow a form of the <em class="firstterm">hacker ethic</em> which dictates that the quest for information and expertise is essential, and that sharing this knowledge is the hackers duty to the community. During this quest for knowledge, some hackers enjoy the academic challenges of circumventing security controls on computer systems. For this reason, the press often uses the term hacker to describe those who illicitly access systems and networks with unscrupulous, malicious, or criminal intent. The more accurate term for this type of computer hacker is <em class="firstterm">cracker</em> — a term created by hackers in the mid-1980s to differentiate the two communities.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-A_Quick_History_of_Hackers-Shades_of_Gray">1.3.1.1. Shades of Gray</h4></div></div></div><a id="d0e972" class="indexterm"/><a id="d0e977" class="indexterm"/><a id="d0e982" class="indexterm"/><a id="d0e989" class="indexterm"/><a id="d0e994" class="indexterm"/><a id="d0e999" class="indexterm"/><a id="d0e1004" class="indexterm"/><div class="para">
Within the community of individuals who find and exploit vulnerabilities in systems and networks are several distinct groups. These groups are often described by the shade of hat that they "wear" when performing their security investigations and this shade is indicative of their intent.
</div><div class="para">
The <em class="firstterm">white hat hacker</em> is one who tests networks and systems to examine their performance and determine how vulnerable they are to intrusion. Usually, white hat hackers crack their own systems or the systems of a client who has specifically employed them for the purposes of security auditing. Academic researchers and professional security consultants are two examples of white hat hackers.
</div><div class="para">
A <em class="firstterm">black hat hacker</em> is synonymous with a cracker. In general, crackers are less focused on programming and the academic side of breaking into systems. They often rely on available cracking programs and exploit well known vulnerabilities in systems to uncover sensitive information for personal gain or to inflict damage on the target system or network.
</div><div class="para">
The <em class="firstterm">gray hat hacker</em>, on the other hand, has the skills and intent of a white hat hacker in most situations but uses his knowledge for less than noble purposes on occasion. A gray hat hacker can be thought of as a white hat hacker who wears a black hat at times to accomplish his own agenda.
</div><div class="para">
Gray hat hackers typically subscribe to another form of the hacker ethic, which says it is acceptable to break into systems as long as the hacker does not commit theft or breach confidentiality. Some would argue, however, that the act of breaking into a system is in itself unethical.
</div><div class="para">
Regardless of the intent of the intruder, it is important to know the weaknesses a cracker may likely attempt to exploit. The remainder of the chapter focuses on these issues.
</div></div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Evaluating_the_Tools-Anticipating_Your_Future_Needs.html"><strong>Prev</strong>1.2.3.5. Anticipating Your Future Needs</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Attackers_and_Vulnerabilities-Threats_to_Network_Security.html"><strong>Next</strong>1.3.2. Threats to Network Security</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.8.2.6. Activating the IPTables Service</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Firewalls-Basic_Firewall_Configuration.html" title="2.8.2. Basic Firewall Configuration"/><link rel="prev" href="sect-Security_Guide-Basic_Firewall_Configuration-Saving_the_Settings.html" title="2.8.2.5. Saving the Settings"/><link rel="next" href="sect-Security_Guide-Firewalls-Using_IPTables.html" title="2.8.3. Using IPTables"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_righ
t.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Basic_Firewall_Configuration-Saving_the_Settings.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Firewalls-Using_IPTables.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Basic_Firewall_Configuration-Activating_the_IPTables_Service">2.8.2.6. Activating the IPTables Service</h4></div></div></div><a id="d0e13140" class="indexterm"/><a id="d0e13148" class="indexterm"/><div class="para">
The firewall rules are only active if the <code class="command">iptables</code> service is running. To manually start the service, use the following command:
</div><pre class="screen">[root@myServer ~] # service iptables restart
</pre><div class="para">
To ensure that <code class="command">iptables</code> starts when the system is booted, use the following command:
</div><pre class="screen">[root@myServer ~] # chkconfig --level 345 iptables on
</pre><div class="para">
The <code class="command">ipchains</code> service is not included in Fedora. However, if <code class="command">ipchains</code> is installed (for example, an upgrade was performed and the system had <code class="command">ipchains</code> previously installed), the <code class="command">ipchains</code> and <code class="command">iptables</code> services should not be activated simultaneously. To make sure the <code class="command">ipchains</code> service is disabled and configured not to start at boot time, use the following two commands:
</div><pre class="screen">[root@myServer ~] # service ipchains stop
[root@myServer ~] # chkconfig --level 345 ipchains off
</pre></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Basic_Firewall_Configuration-Saving_the_Settings.html"><strong>Prev</strong>2.8.2.5. Saving the Settings</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Firewalls-Using_IPTables.html"><strong>Next</strong>2.8.3. Using IPTables</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.8.2.2. Enabling and Disabling the Firewall</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Firewalls-Basic_Firewall_Configuration.html" title="2.8.2. Basic Firewall Configuration"/><link rel="prev" href="sect-Security_Guide-Firewalls-Basic_Firewall_Configuration.html" title="2.8.2. Basic Firewall Configuration"/><link rel="next" href="sect-Security_Guide-Basic_Firewall_Configuration-Trusted_Services.html" title="2.8.2.3. Trusted Services"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common
_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Firewalls-Basic_Firewall_Configuration.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Basic_Firewall_Configuration-Trusted_Services.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Basic_Firewall_Configuration-Enabling_and_Disabling_the_Firewall">2.8.2.2. Enabling and Disabling the Firewall</h4></div></div></div><a id="d0e12938" class="indexterm"/><div class="para">
Select one of the following options for the firewall:
</div><div class="itemizedlist"><ul><li><div class="para">
<span class="guilabel"><strong>Disabled</strong></span> — Disabling the firewall provides complete access to your system and does no security checking. This should only be selected if you are running on a trusted network (not the Internet) or need to configure a custom firewall using the iptables command line tool.
</div><div class="warning"><h2>Warning</h2><div class="para">
Firewall configurations and any customized firewall rules are stored in the <code class="filename">/etc/sysconfig/iptables</code> file. If you choose <span class="guilabel"><strong>Disabled</strong></span> and click <span class="guibutton"><strong>OK</strong></span>, these configurations and firewall rules will be lost.
</div></div></li><li><div class="para">
<span class="guilabel"><strong>Enabled</strong></span> — This option configures the system to reject incoming connections that are not in response to outbound requests, such as DNS replies or DHCP requests. If access to services running on this machine is needed, you can choose to allow specific services through the firewall.
</div><div class="para">
If you are connecting your system to the Internet, but do not plan to run a server, this is the safest choice.
</div></li></ul></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Firewalls-Basic_Firewall_Configuration.html"><strong>Prev</strong>2.8.2. Basic Firewall Configuration</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Basic_Firewall_Configuration-Trusted_Services.html"><strong>Next</strong>2.8.2.3. Trusted Services</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.8.2.4. Other Ports</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Firewalls-Basic_Firewall_Configuration.html" title="2.8.2. Basic Firewall Configuration"/><link rel="prev" href="sect-Security_Guide-Basic_Firewall_Configuration-Trusted_Services.html" title="2.8.2.3. Trusted Services"/><link rel="next" href="sect-Security_Guide-Basic_Firewall_Configuration-Saving_the_Settings.html" title="2.8.2.5. Saving the Settings"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image
_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Basic_Firewall_Configuration-Trusted_Services.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Basic_Firewall_Configuration-Saving_the_Settings.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Basic_Firewall_Configuration-Other_Ports">2.8.2.4. Other Ports</h4></div></div></div><a id="d0e13065" class="indexterm"/><div class="para">
The <span class="application"><strong>Security Level Configuration Tool</strong></span> includes an <span class="guilabel"><strong>Other ports</strong></span> section for specifying custom IP ports as being trusted by <code class="command">iptables</code>. For example, to allow IRC and Internet printing protocol (IPP) to pass through the firewall, add the following to the <span class="guilabel"><strong>Other ports</strong></span> section:
</div><div class="para">
<code class="computeroutput">194:tcp,631:tcp</code>
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Basic_Firewall_Configuration-Trusted_Services.html"><strong>Prev</strong>2.8.2.3. Trusted Services</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Basic_Firewall_Configuration-Saving_the_Settings.html"><strong>Next</strong>2.8.2.5. Saving the Settings</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.8.2.5. Saving the Settings</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Firewalls-Basic_Firewall_Configuration.html" title="2.8.2. Basic Firewall Configuration"/><link rel="prev" href="sect-Security_Guide-Basic_Firewall_Configuration-Other_Ports.html" title="2.8.2.4. Other Ports"/><link rel="next" href="sect-Security_Guide-Basic_Firewall_Configuration-Activating_the_IPTables_Service.html" title="2.8.2.6. Activating the IPTables Service"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Commo
n_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Basic_Firewall_Configuration-Other_Ports.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Basic_Firewall_Configuration-Activating_the_IPTables_Service.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Basic_Firewall_Configuration-Saving_the_Settings">2.8.2.5. Saving the Settings</h4></div></div></div><a id="d0e13093" class="indexterm"/><div class="para">
Click <span class="guibutton"><strong>OK</strong></span> to save the changes and enable or disable the firewall. If <span class="guilabel"><strong>Enable firewall</strong></span> was selected, the options selected are translated to <code class="command">iptables</code> commands and written to the <code class="filename">/etc/sysconfig/iptables</code> file. The <code class="command">iptables</code> service is also started so that the firewall is activated immediately after saving the selected options. If <span class="guilabel"><strong>Disable firewall</strong></span> was selected, the <code class="filename">/etc/sysconfig/iptables</code> file is removed and the <code class="command">iptables</code> service is stopped immediately.
</div><div class="para">
The selected options are also written to the <code class="filename">/etc/sysconfig/system-config-securitylevel</code> file so that the settings can be restored the next time the application is started. Do not edit this file by hand.
</div><div class="para">
Even though the firewall is activated immediately, the <code class="command">iptables</code> service is not configured to start automatically at boot time. Refer to <a class="xref" href="sect-Security_Guide-Basic_Firewall_Configuration-Activating_the_IPTables_Service.html" title="2.8.2.6. Activating the IPTables Service">Section 2.8.2.6, “Activating the IPTables Service”</a> for more information.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Basic_Firewall_Configuration-Other_Ports.html"><strong>Prev</strong>2.8.2.4. Other Ports</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Basic_Firewall_Configuration-Activating_the_IPTables_Service.html"><strong>Next</strong>2.8.2.6. Activating the IPTables Service</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.8.2.3. Trusted Services</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Firewalls-Basic_Firewall_Configuration.html" title="2.8.2. Basic Firewall Configuration"/><link rel="prev" href="sect-Security_Guide-Basic_Firewall_Configuration-Enabling_and_Disabling_the_Firewall.html" title="2.8.2.2. Enabling and Disabling the Firewall"/><link rel="next" href="sect-Security_Guide-Basic_Firewall_Configuration-Other_Ports.html" title="2.8.2.4. Other Ports"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="
Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Basic_Firewall_Configuration-Enabling_and_Disabling_the_Firewall.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Basic_Firewall_Configuration-Other_Ports.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Basic_Firewall_Configuration-Trusted_Services">2.8.2.3. Trusted Services</h4></div></div></div><a id="d0e12978" class="indexterm"/><div class="para">
Enabling options in the <span class="guilabel"><strong>Trusted services</strong></span> list allows the specified service to pass through the firewall.
</div><div class="variablelist"><dl><dt><span class="term"><span class="guilabel"><strong>WWW (HTTP)</strong></span></span></dt><dd><div class="para">
The HTTP protocol is used by Apache (and by other Web servers) to serve web pages. If you plan on making your Web server publicly available, select this check box. This option is not required for viewing pages locally or for developing web pages. This service requires that the <code class="filename">httpd</code> package be installed.
</div><div class="para">
Enabling <span class="guilabel"><strong>WWW (HTTP)</strong></span> will not open a port for HTTPS, the SSL version of HTTP. If this service is required, select the <span class="guilabel"><strong>Secure WWW (HTTPS)</strong></span> check box.
</div></dd><dt><span class="term"><span class="guilabel"><strong>FTP</strong></span></span></dt><dd><div class="para">
The FTP protocol is used to transfer files between machines on a network. If you plan on making your FTP server publicly available, select this check box. This service requires that the <code class="filename">vsftpd</code> package be installed.
</div></dd><dt><span class="term"><span class="guilabel"><strong>SSH</strong></span></span></dt><dd><div class="para">
Secure Shell (SSH) is a suite of tools for logging into and executing commands on a remote machine. To allow remote access to the machine via ssh, select this check box. This service requires that the <code class="filename">openssh-server</code> package be installed.
</div></dd><dt><span class="term"><span class="guilabel"><strong>Telnet</strong></span></span></dt><dd><div class="para">
Telnet is a protocol for logging into remote machines. Telnet communications are unencrypted and provide no security from network snooping. Allowing incoming Telnet access is not recommended. To allow remote access to the machine via telnet, select this check box. This service requires that the <code class="filename">telnet-server</code> package be installed.
</div></dd><dt><span class="term"><span class="guilabel"><strong>Mail (SMTP)</strong></span></span></dt><dd><div class="para">
SMTP is a protocol that allows remote hosts to connect directly to your machine to deliver mail. You do not need to enable this service if you collect your mail from your ISP's server using POP3 or IMAP, or if you use a tool such as <code class="command">fetchmail</code>. To allow delivery of mail to your machine, select this check box. Note that an improperly configured SMTP server can allow remote machines to use your server to send spam.
</div></dd><dt><span class="term"><span class="guilabel"><strong>NFS4</strong></span></span></dt><dd><div class="para">
The Network File System (NFS) is a file sharing protocol commonly used on *NIX systems. Version 4 of this protocol is more secure than its predecessors. If you want to share files or directories on your system with other network users, select this check box.
</div></dd><dt><span class="term"><span class="guilabel"><strong>Samba</strong></span></span></dt><dd><div class="para">
Samba is an implementation of Microsoft's proprietary SMB networking protocol. If you need to share files, directories, or locally-connected printers with Microsoft Windows machines, select this check box.
</div></dd></dl></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Basic_Firewall_Configuration-Enabling_and_Disabling_the_Firewall.html"><strong>Prev</strong>2.8.2.2. Enabling and Disabling the Firewall</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Basic_Firewall_Configuration-Other_Ports.html"><strong>Next</strong>2.8.2.4. Other Ports</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.9.3.2. Command Options</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-IPTables-Command_Options_for_IPTables.html" title="2.9.3. Command Options for IPTables"/><link rel="prev" href="sect-Security_Guide-IPTables-Command_Options_for_IPTables.html" title="2.9.3. Command Options for IPTables"/><link rel="next" href="sect-Security_Guide-Command_Options_for_IPTables-IPTables_Parameter_Options.html" title="2.9.3.3. IPTables Parameter Options"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_C
ontent/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-IPTables-Command_Options_for_IPTables.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Command_Options_for_IPTables-IPTables_Parameter_Options.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Command_Options_for_IPTables-Command_Options">2.9.3.2. Command Options</h4></div></div></div><a id="d0e14492" class="indexterm"/><div class="para">
Command options instruct <code class="command">iptables</code> to perform a specific action. Only one command option is allowed per <code class="command">iptables</code> command. With the exception of the help command, all commands are written in upper-case characters.
</div><div class="para">
The <code class="command">iptables</code> commands are as follows:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">-A</code> — Appends the rule to the end of the specified chain. Unlike the <code class="option">-I</code> option described below, it does not take an integer argument. It always appends the rule to the end of the specified chain.
</div></li><li><div class="para">
<code class="option">-C</code> — Checks a particular rule before adding it to the user-specified chain. This command can help you construct complex <code class="command">iptables</code> rules by prompting you for additional parameters and options.
</div></li><li><div class="para">
<code class="option">-D <integer> | <rule></code> — Deletes a rule in a particular chain by number (such as <code class="option">5</code> for the fifth rule in a chain), or by rule specification. The rule specification must exactly match an existing rule.
</div></li><li><div class="para">
<code class="option">-E</code> — Renames a user-defined chain. A user-defined chain is any chain other than the default, pre-existing chains. (Refer to the <code class="option">-N</code> option, below, for information on creating user-defined chains.) This is a cosmetic change and does not affect the structure of the table.
</div><div class="note"><h2>Note</h2><div class="para">
If you attempt to rename one of the default chains, the system reports a <code class="computeroutput">Match not found</code> error. You cannot rename the default chains.
</div></div></li><li><div class="para">
<code class="option">-F</code> — Flushes the selected chain, which effectively deletes every rule in the chain. If no chain is specified, this command flushes every rule from every chain.
</div></li><li><div class="para">
<code class="option">-h</code> — Provides a list of command structures, as well as a quick summary of command parameters and options.
</div></li><li><div class="para">
<code class="option">-I [<integer>]</code> — Inserts the rule in the specified chain at a point specified by a user-defined integer argument. If no argument is specified, the rule is inserted at the top of the chain.
</div><div class="caution"><h2>Caution</h2><div class="para">
As noted above, the order of rules in a chain determines which rules apply to which packets. This is important to remember when adding rules using either the <code class="option">-A</code> or <code class="option">-I</code> option.
</div><div class="para">
This is especially important when adding rules using the <code class="option">-I</code> with an integer argument. If you specify an existing number when adding a rule to a chain, <code class="command">iptables</code> adds the new rule <span class="emphasis"><em>before</em></span> (or above) the existing rule.
</div></div></li><li><div class="para">
<code class="option">-L</code> — Lists all of the rules in the chain specified after the command. To list all rules in all chains in the default <code class="option">filter</code> table, do not specify a chain or table. Otherwise, the following syntax should be used to list the rules in a specific chain in a particular table:
</div><pre class="screen"><code class="computeroutput"> iptables -L <em class="replaceable"><code><chain-name></code></em> -t <em class="replaceable"><code><table-name></code></em></code>
</pre><div class="para">
Additional options for the <code class="option">-L</code> command option, which provide rule numbers and allow more verbose rule descriptions, are described in <a class="xref" href="sect-Security_Guide-Command_Options_for_IPTables-Listing_Options.html" title="2.9.3.6. Listing Options">Section 2.9.3.6, “Listing Options”</a>.
</div></li><li><div class="para">
<code class="option">-N</code> — Creates a new chain with a user-specified name. The chain name must be unique, otherwise an error message is displayed.
</div></li><li><div class="para">
<code class="option">-P</code> — Sets the default policy for the specified chain, so that when packets traverse an entire chain without matching a rule, they are sent to the specified target, such as ACCEPT or DROP.
</div></li><li><div class="para">
<code class="option">-R</code> — Replaces a rule in the specified chain. The rule's number must be specified after the chain's name. The first rule in a chain corresponds to rule number one.
</div></li><li><div class="para">
<code class="option">-X</code> — Deletes a user-specified chain. You cannot delete a built-in chain.
</div></li><li><div class="para">
<code class="option">-Z</code> — Sets the byte and packet counters in all chains for a table to zero.
</div></li></ul></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-IPTables-Command_Options_for_IPTables.html"><strong>Prev</strong>2.9.3. Command Options for IPTables</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Command_Options_for_IPTables-IPTables_Parameter_Options.html"><strong>Next</strong>2.9.3.3. IPTables Parameter Options</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.9.3.4. IPTables Match Options</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-IPTables-Command_Options_for_IPTables.html" title="2.9.3. Command Options for IPTables"/><link rel="prev" href="sect-Security_Guide-Command_Options_for_IPTables-IPTables_Parameter_Options.html" title="2.9.3.3. IPTables Parameter Options"/><link rel="next" href="sect-Security_Guide-IPTables_Match_Options-UDP_Protocol.html" title="2.9.3.4.2. UDP Protocol"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/
images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Command_Options_for_IPTables-IPTables_Parameter_Options.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables_Match_Options-UDP_Protocol.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Command_Options_for_IPTables-IPTables_Match_Options">2.9.3.4. IPTables Match Options</h4></div></div></div><a id="d0e14889" class="indexterm"/><div class="para">
Different network protocols provide specialized matching options which can be configured to match a particular packet using that protocol. However, the protocol must first be specified in the <code class="command">iptables</code> command. For example, <code class="option">-p <em class="replaceable"><code><protocol-name></code></em></code> enables options for the specified protocol. Note that you can also use the protocol ID, instead of the protocol name. Refer to the following examples, each of which have the same effect:
</div><pre class="screen"><code class="command"> iptables -A INPUT -p icmp --icmp-type any -j ACCEPT </code><code class="command"> iptables -A INPUT -p 5813 --icmp-type any -j ACCEPT </code>
</pre><div class="para">
Service definitions are provided in the <code class="filename">/etc/services</code> file. For readability, it is recommended that you use the service names rather than the port numbers.
</div><div class="important"><h2>Important</h2><div class="para">
Secure the <code class="filename">/etc/services</code> file to prevent unauthorized editing. If this file is editable, crackers can use it to enable ports on your machine you have otherwise closed. To secure this file, type the following commands as root:
</div><pre class="screen"><code class="command"> [root@myServer ~]# chown root.root /etc/services [root@myServer ~]# chmod 0644 /etc/services [root@myServer ~]# chattr +i /etc/services </code>
</pre><div class="para">
This prevents the file from being renamed, deleted or having links made to it.
</div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-IPTables_Match_Options-TCP_Protocol">2.9.3.4.1. TCP Protocol</h5></div></div></div><a id="d0e14933" class="indexterm"/><div class="para">
These match options are available for the TCP protocol (<code class="option">-p tcp</code>):
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">--dport</code> — Sets the destination port for the packet.
</div><div class="para">
To configure this option, use a network service name (such as www or smtp); a port number; or a range of port numbers.
</div><div class="para">
To specify a range of port numbers, separate the two numbers with a colon (<code class="option">:</code>). For example: <code class="option">-p tcp --dport 3000:3200</code>. The largest acceptable valid range is <code class="option">0:65535</code>.
</div><div class="para">
Use an exclamation point character (<code class="option">!</code>) after the <code class="option">--dport</code> option to match all packets that <span class="emphasis"><em>do not</em></span> use that network service or port.
</div><div class="para">
To browse the names and aliases of network services and the port numbers they use, view the <code class="filename">/etc/services</code> file.
</div><div class="para">
The <code class="option">--destination-port</code> match option is synonymous with <code class="option">--dport</code>.
</div></li><li><div class="para">
<code class="option">--sport</code> — Sets the source port of the packet using the same options as <code class="option">--dport</code>. The <code class="option">--source-port</code> match option is synonymous with <code class="option">--sport</code>.
</div></li><li><div class="para">
<code class="option">--syn</code> — Applies to all TCP packets designed to initiate communication, commonly called <em class="firstterm">SYN packets</em>. Any packets that carry a data payload are not touched.
</div><div class="para">
Use an exclamation point character (<code class="option">!</code>) after the <code class="option">--syn</code> option to match all non-SYN packets.
</div></li><li><div class="para">
<code class="option">--tcp-flags <tested flag list> <set flag list></code> — Allows TCP packets that have specific bits (flags) set, to match a rule.
</div><div class="para">
The <code class="option">--tcp-flags</code> match option accepts two parameters. The first parameter is the mask; a comma-separated list of flags to be examined in the packet. The second parameter is a comma-separated list of flags that must be set for the rule to match.
</div><div class="para">
The possible flags are:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">ACK</code>
</div></li><li><div class="para">
<code class="option">FIN</code>
</div></li><li><div class="para">
<code class="option">PSH</code>
</div></li><li><div class="para">
<code class="option">RST</code>
</div></li><li><div class="para">
<code class="option">SYN</code>
</div></li><li><div class="para">
<code class="option">URG</code>
</div></li><li><div class="para">
<code class="option">ALL</code>
</div></li><li><div class="para">
<code class="option">NONE</code>
</div></li></ul></div><div class="para">
For example, an <code class="command">iptables</code> rule that contains the following specification only matches TCP packets that have the SYN flag set and the ACK and FIN flags not set:
</div><div class="para">
<code class="command">--tcp-flags ACK,FIN,SYN SYN</code>
</div><div class="para">
Use the exclamation point character (<code class="option">!</code>) after the <code class="option">--tcp-flags</code> to reverse the effect of the match option.
</div></li><li><div class="para">
<code class="option">--tcp-option</code> — Attempts to match with TCP-specific options that can be set within a particular packet. This match option can also be reversed with the exclamation point character (<code class="option">!</code>).
</div></li></ul></div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Command_Options_for_IPTables-IPTables_Parameter_Options.html"><strong>Prev</strong>2.9.3.3. IPTables Parameter Options</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables_Match_Options-UDP_Protocol.html"><strong>Next</strong>2.9.3.4.2. UDP Protocol</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.9.3.3. IPTables Parameter Options</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-IPTables-Command_Options_for_IPTables.html" title="2.9.3. Command Options for IPTables"/><link rel="prev" href="sect-Security_Guide-Command_Options_for_IPTables-Command_Options.html" title="2.9.3.2. Command Options"/><link rel="next" href="sect-Security_Guide-Command_Options_for_IPTables-IPTables_Match_Options.html" title="2.9.3.4. IPTables Match Options"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Co
ntent/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Command_Options_for_IPTables-Command_Options.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Command_Options_for_IPTables-IPTables_Match_Options.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Command_Options_for_IPTables-IPTables_Parameter_Options">2.9.3.3. IPTables Parameter Options</h4></div></div></div><a id="d0e14656" class="indexterm"/><div class="para">
Certain <code class="command">iptables</code> commands, including those used to add, append, delete, insert, or replace rules within a particular chain, require various parameters to construct a packet filtering rule.
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">-c</code> — Resets the counters for a particular rule. This parameter accepts the <code class="option">PKTS</code> and <code class="option">BYTES</code> options to specify which counter to reset.
</div></li><li><div class="para">
<code class="option">-d</code> — Sets the destination hostname, IP address, or network of a packet that matches the rule. When matching a network, the following IP address/netmask formats are supported:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option"><em class="replaceable"><code>N.N.N.N</code></em>/<em class="replaceable"><code>M.M.M.M</code></em></code> — Where <em class="replaceable"><code>N.N.N.N</code></em> is the IP address range and <em class="replaceable"><code>M.M.M.M</code></em> is the netmask.
</div></li><li><div class="para">
<code class="option"><em class="replaceable"><code>N.N.N.N</code></em>/<em class="replaceable"><code>M</code></em></code> — Where <em class="replaceable"><code>N.N.N.N</code></em> is the IP address range and <em class="replaceable"><code>M</code></em> is the bitmask.
</div></li></ul></div></li><li><div class="para">
<code class="option">-f</code> — Applies this rule only to fragmented packets.
</div><div class="para">
You can use the exclamation point character (<code class="option">!</code>) option after this parameter to specify that only unfragmented packets are matched.
</div><div class="note"><h2>Note</h2><div class="para">
Distinguishing between fragmented and unfragmented packets is desirable, despite fragmented packets being a standard part of the IP protocol.
</div><div class="para">
Originally designed to allow IP packets to travel over networks with differing frame sizes, these days fragmentation is more commonly used to generate DoS attacks using mal-formed packets. It's also worth noting that IPv6 disallows fragmentation entirely.
</div></div></li><li><div class="para">
<code class="option">-i</code> — Sets the incoming network interface, such as <code class="option">eth0</code> or <code class="option">ppp0</code>. With <code class="command">iptables</code>, this optional parameter may only be used with the INPUT and FORWARD chains when used with the <code class="option">filter</code> table and the PREROUTING chain with the <code class="option">nat</code> and <code class="option">mangle</code> tables.
</div><div class="para">
This parameter also supports the following special options:
</div><div class="itemizedlist"><ul><li><div class="para">
Exclamation point character (<code class="option">!</code>) — Reverses the directive, meaning any specified interfaces are excluded from this rule.
</div></li><li><div class="para">
Plus character (<code class="option">+</code>) — A wildcard character used to match all interfaces that match the specified string. For example, the parameter <code class="option">-i eth+</code> would apply this rule to any Ethernet interfaces but exclude any other interfaces, such as <code class="option">ppp0</code>.
</div></li></ul></div><div class="para">
If the <code class="option">-i</code> parameter is used but no interface is specified, then every interface is affected by the rule.
</div></li><li><div class="para">
<code class="option">-j</code> — Jumps to the specified target when a packet matches a particular rule.
</div><div class="para">
The standard targets are <code class="option">ACCEPT</code>, <code class="option">DROP</code>, <code class="option">QUEUE</code>, and <code class="option">RETURN</code>.
</div><div class="para">
Extended options are also available through modules loaded by default with the Fedora <code class="command">iptables</code> RPM package. Valid targets in these modules include <code class="option">LOG</code>, <code class="option">MARK</code>, and <code class="option">REJECT</code>, among others. Refer to the <code class="command">iptables</code> man page for more information about these and other targets.
</div><div class="para">
This option can also be used to direct a packet matching a particular rule to a user-defined chain outside of the current chain so that other rules can be applied to the packet.
</div><div class="para">
If no target is specified, the packet moves past the rule with no action taken. The counter for this rule, however, increases by one.
</div></li><li><div class="para">
<code class="option">-o</code> — Sets the outgoing network interface for a rule. This option is only valid for the OUTPUT and FORWARD chains in the <code class="option">filter</code> table, and the POSTROUTING chain in the <code class="option">nat</code> and <code class="option">mangle</code> tables. This parameter accepts the same options as the incoming network interface parameter (<code class="option">-i</code>).
</div></li><li><div class="para">
<code class="option">-p <protocol></code> — Sets the IP protocol affected by the rule. This can be either <code class="option">icmp</code>, <code class="option">tcp</code>, <code class="option">udp</code>, or <code class="option">all</code>, or it can be a numeric value, representing one of these or a different protocol. You can also use any protocols listed in the <code class="filename">/etc/protocols</code> file.
</div><div class="para">
The "<code class="option">all</code>" protocol means the rule applies to every supported protocol. If no protocol is listed with this rule, it defaults to "<code class="option">all</code>".
</div></li><li><div class="para">
<code class="option">-s</code> — Sets the source for a particular packet using the same syntax as the destination (<code class="option">-d</code>) parameter.
</div></li></ul></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Command_Options_for_IPTables-Command_Options.html"><strong>Prev</strong>2.9.3.2. Command Options</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Command_Options_for_IPTables-IPTables_Match_Options.html"><strong>Next</strong>2.9.3.4. IPTables Match Options</a></li></ul></body></html>
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cumentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Command_Options_for_IPTables-Target_Options.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables-Saving_IPTables_Rules.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Command_Options_for_IPTables-Listing_Options">2.9.3.6. Listing Options</h4></div></div></div><a id="d0e15519" class="indexterm"/><div class="para">
The default list command, <code class="command">iptables -L [<chain-name>]</code>, provides a very basic overview of the default filter table's current chains. Additional options provide more information:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">-v</code> — Displays verbose output, such as the number of packets and bytes each chain has processed, the number of packets and bytes each rule has matched, and which interfaces apply to a particular rule.
</div></li><li><div class="para">
<code class="option">-x</code> — Expands numbers into their exact values. On a busy system, the number of packets and bytes processed by a particular chain or rule may be abbreviated to <code class="computeroutput">Kilobytes</code>, <code class="computeroutput">Megabytes</code> (Megabytes) or <code class="computeroutput">Gigabytes</code>. This option forces the full number to be displayed.
</div></li><li><div class="para">
<code class="option">-n</code> — Displays IP addresses and port numbers in numeric format, rather than the default hostname and network service format.
</div></li><li><div class="para">
<code class="option">--line-numbers</code> — Lists rules in each chain next to their numeric order in the chain. This option is useful when attempting to delete the specific rule in a chain or to locate where to insert a rule within a chain.
</div></li><li><div class="para">
<code class="option">-t <table-name></code> — Specifies a table name. If omitted, defaults to the filter table.
</div></li></ul></div><div class="para">
The following examples illustrate the use of several of these options. Note the difference in the byte display by including the <code class="option">-x</code> option.
</div><pre class="screen"><code class="computeroutput"> [root@myserver ~]# iptables -L OUTPUT -v -n -x Chain OUTPUT (policy ACCEPT 64005 packets, 6445791 bytes) pkts bytes target prot opt in out source destination 1593 133812 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 [root@myserver ~]#iptables -L OUTPUT -v -n Chain OUTPUT (policy ACCEPT 64783 packets, 6492K bytes) pkts bytes target prot opt in out source destination 1819 153K ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 [root@myserver ~]# </code>
</pre></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Command_Options_for_IPTables-Target_Options.html"><strong>Prev</strong>2.9.3.5. Target Options</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables-Saving_IPTables_Rules.html"><strong>Next</strong>2.9.4. Saving IPTables Rules</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.9.3.5. Target Options</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-IPTables-Command_Options_for_IPTables.html" title="2.9.3. Command Options for IPTables"/><link rel="prev" href="sect-Security_Guide-IPTables_Match_Options-Additional_Match_Option_Modules.html" title="2.9.3.4.4. Additional Match Option Modules"/><link rel="next" href="sect-Security_Guide-Command_Options_for_IPTables-Listing_Options.html" title="2.9.3.6. Listing Options"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_
Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-IPTables_Match_Options-Additional_Match_Option_Modules.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Command_Options_for_IPTables-Listing_Options.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Command_Options_for_IPTables-Target_Options">2.9.3.5. Target Options</h4></div></div></div><a id="d0e15360" class="indexterm"/><div class="para">
When a packet has matched a particular rule, the rule can direct the packet to a number of different targets which determine the appropriate action. Each chain has a default target, which is used if none of the rules on that chain match a packet or if none of the rules which match the packet specify a target.
</div><div class="para">
The following are the standard targets:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option"><em class="replaceable"><code><user-defined-chain></code></em></code> — A user-defined chain within the table. User-defined chain names must be unique. This target passes the packet to the specified chain.
</div></li><li><div class="para">
<code class="option">ACCEPT</code> — Allows the packet through to its destination or to another chain.
</div></li><li><div class="para">
<code class="option">DROP</code> — Drops the packet without responding to the requester. The system that sent the packet is not notified of the failure.
</div></li><li><div class="para">
<code class="option">QUEUE</code> — The packet is queued for handling by a user-space application.
</div></li><li><div class="para">
<code class="option">RETURN</code> — Stops checking the packet against rules in the current chain. If the packet with a <code class="option">RETURN</code> target matches a rule in a chain called from another chain, the packet is returned to the first chain to resume rule checking where it left off. If the <code class="option">RETURN</code> rule is used on a built-in chain and the packet cannot move up to its previous chain, the default target for the current chain is used.
</div></li></ul></div><div class="para">
In addition, extensions are available which allow other targets to be specified. These extensions are called target modules or match option modules and most only apply to specific tables and situations. Refer to <a class="xref" href="sect-Security_Guide-IPTables_Match_Options-Additional_Match_Option_Modules.html" title="2.9.3.4.4. Additional Match Option Modules">Section 2.9.3.4.4, “Additional Match Option Modules”</a> for more information about match option modules.
</div><div class="para">
Many extended target modules exist, most of which only apply to specific tables or situations. Some of the most popular target modules included by default in Fedora are:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">LOG</code> — Logs all packets that match this rule. Because the packets are logged by the kernel, the <code class="filename">/etc/syslog.conf</code> file determines where these log entries are written. By default, they are placed in the <code class="filename">/var/log/messages</code> file.
</div><div class="para">
Additional options can be used after the <code class="option">LOG</code> target to specify the way in which logging occurs:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">--log-level</code> — Sets the priority level of a logging event. Refer to the <code class="filename">syslog.conf</code> man page for a list of priority levels.
</div></li><li><div class="para">
<code class="option">--log-ip-options</code> — Logs any options set in the header of an IP packet.
</div></li><li><div class="para">
<code class="option">--log-prefix</code> — Places a string of up to 29 characters before the log line when it is written. This is useful for writing syslog filters for use in conjunction with packet logging.
</div><div class="note"><h2>Note</h2><div class="para">
Due to an issue with this option, you should add a trailing space to the <em class="replaceable"><code>log-prefix</code></em> value.
</div></div></li><li><div class="para">
<code class="option">--log-tcp-options</code> — Logs any options set in the header of a TCP packet.
</div></li><li><div class="para">
<code class="option">--log-tcp-sequence</code> — Writes the TCP sequence number for the packet in the log.
</div></li></ul></div></li><li><div class="para">
<code class="option">REJECT</code> — Sends an error packet back to the remote system and drops the packet.
</div><div class="para">
The <code class="option">REJECT</code> target accepts <code class="option">--reject-with <em class="replaceable"><code><type></code></em></code> (where <em class="replaceable"><code><type></code></em> is the rejection type) allowing more detailed information to be returned with the error packet. The message <code class="computeroutput">port-unreachable</code> is the default error type given if no other option is used. Refer to the <code class="command">iptables</code> man page for a full list of <code class="option"><em class="replaceable"><code><type></code></em></code> options.
</div></li></ul></div><div class="para">
Other target extensions, including several that are useful for IP masquerading using the <code class="option">nat</code> table, or with packet alteration using the <code class="option">mangle</code> table, can be found in the <code class="command">iptables</code> man page.
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>1.4. Common Exploits and Attacks</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="chap-Security_Guide-Security_Overview.html" title="Chapter 1. Security Overview"/><link rel="prev" href="sect-Security_Guide-Threats_to_Workstation_and_Home_PC_Security-Vulnerable_Client_Applications.html" title="1.3.4.2. Vulnerable Client Applications"/><link rel="next" href="sect-Security_Guide-Security_Updates.html" title="1.5. Security Updates"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png"
alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Threats_to_Workstation_and_Home_PC_Security-Vulnerable_Client_Applications.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Security_Updates.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-Common_Exploits_and_Attacks">1.4. Common Exploits and Attacks</h2></div></div></div><a id="d0e1212" class="indexterm"/><a id="d0e1217" class="indexterm"/><div class="para">
<a class="xref" href="sect-Security_Guide-Common_Exploits_and_Attacks.html#tabl-Security_Guide-Common_Exploits_and_Attacks-Common_Exploits" title="Table 1.1. Common Exploits">Table 1.1, “Common Exploits”</a> details some of the most common exploits and entry points used by intruders to access organizational network resources. Key to these common exploits are the explanations of how they are performed and how administrators can properly safeguard their network against such attacks.
</div><div class="table" id="tabl-Security_Guide-Common_Exploits_and_Attacks-Common_Exploits"><div class="table-contents"><table summary="Common Exploits" border="1"><colgroup><col width="2*"/><col width="4*"/><col width="4*"/></colgroup><thead><tr><th>
Exploit
</th><th>
Description
</th><th>
Notes
</th></tr></thead><tbody><tr><td>
Null or Default Passwords
</td><td>
Leaving administrative passwords blank or using a default password set by the product vendor. This is most common in hardware such as routers and firewalls, though some services that run on Linux can contain default administrator passwords (though Fedora 5 does not ship with them).
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> Commonly associated with networking hardware such as routers, firewalls, VPNs, and network attached storage (NAS) appliances. </td></tr><tr><td> Common in many legacy operating systems, especially OSes that bundle services (such as UNIX and Windows.) </td></tr><tr><td> Administrators sometimes create privileged user accounts in a rush and leave the password null, a perfect entry point for malicious users who discover the account. </td></tr></table>
</td></tr><tr><td>
Default Shared Keys
</td><td>
Secure services sometimes package default security keys for development or evaluation testing purposes. If these keys are left unchanged and are placed in a production environment on the Internet, <span class="emphasis"><em>all</em></span> users with the same default keys have access to that shared-key resource, and any sensitive information that it contains.
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> Most common in wireless access points and preconfigured secure server appliances. </td></tr></table>
</td></tr><tr><td>
IP Spoofing
</td><td>
A remote machine acts as a node on your local network, finds vulnerabilities with your servers, and installs a backdoor program or trojan horse to gain control over your network resources.
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> Spoofing is quite difficult as it involves the attacker predicting TCP/IP SYN-ACK numbers to coordinate a connection to target systems, but several tools are available to assist crackers in performing such a vulnerability. </td></tr><tr><td> Depends on target system running services (such as <code class="command">rsh</code>, <code class="command">telnet</code>, FTP and others) that use <em class="firstterm">source-based</em> authentication techniques, which are not recommended when compared to PKI or other forms of encrypted authentication used in <code class="command">ssh</code> or SSL/TLS. </td></tr></table>
</td></tr><tr><td>
Eavesdropping
</td><td>
Collecting data that passes between two active nodes on a network by eavesdropping on the connection between the two nodes.
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> This type of attack works mostly with plain text transmission protocols such as Telnet, FTP, and HTTP transfers. </td></tr><tr><td> Remote attacker must have access to a compromised system on a LAN in order to perform such an attack; usually the cracker has used an active attack (such as IP spoofing or man-in-the-middle) to compromise a system on the LAN. </td></tr><tr><td> Preventative measures include services with cryptographic key exchange, one-time passwords, or encrypted authentication to prevent password snooping; strong encryption during transmission is also advised. </td></tr></table>
</td></tr><tr><td>
Service Vulnerabilities
</td><td>
An attacker finds a flaw or loophole in a service run over the Internet; through this vulnerability, the attacker compromises the entire system and any data that it may hold, and could possibly compromise other systems on the network.
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> HTTP-based services such as CGI are vulnerable to remote command execution and even interactive shell access. Even if the HTTP service runs as a non-privileged user such as "nobody", information such as configuration files and network maps can be read, or the attacker can start a denial of service attack which drains system resources or renders it unavailable to other users. </td></tr><tr><td> Services sometimes can have vulnerabilities that go unnoticed during development and testing; these vulnerabilities (such as <em class="firstterm">buffer overflows</em>, where attackers crash a service using arbitary values that fill the memory buffer of an application, giving the attacker an interactive command prompt from which they may execute arbitrary commands) can give complete administrative control to an attacker. </td></tr><tr><td> Administrators should make sure that services do not run as the root user,
and should stay vigilant of patches and errata updates for applications from vendors or security organizations such as CERT and CVE. </td></tr></table>
</td></tr><tr><td>
Application Vulnerabilities
</td><td>
Attackers find faults in desktop and workstation applications (such as e-mail clients) and execute arbitrary code, implant trojan horses for future compromise, or crash systems. Further exploitation can occur if the compromised workstation has administrative privileges on the rest of the network.
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> Workstations and desktops are more prone to exploitation as workers do not have the expertise or experience to prevent or detect a compromise; it is imperative to inform individuals of the risks they are taking when they install unauthorized software or open unsolicited email attachments. </td></tr><tr><td> Safeguards can be implemented such that email client software does not automatically open or execute attachments. Additionally, the automatic update of workstation software via Red Hat Network or other system management services can alleviate the burdens of multi-seat security deployments. </td></tr></table>
</td></tr><tr><td>
Denial of Service (DoS) Attacks
</td><td>
Attacker or group of attackers coordinate against an organization's network or server resources by sending unauthorized packets to the target host (either server, router, or workstation). This forces the resource to become unavailable to legitimate users.
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> The most reported DoS case in the US occurred in 2000. Several highly-trafficked commercial and government sites were rendered unavailable by a coordinated ping flood attack using several compromised systems with high bandwidth connections acting as <em class="firstterm">zombies</em>, or redirected broadcast nodes. </td></tr><tr><td> Source packets are usually forged (as well as rebroadcasted), making investigation as to the true source of the attack difficult. </td></tr><tr><td> Advances in ingress filtering (IETF rfc2267) using <code class="command">iptables</code> and Network IDSes such as <code class="command">snort</code> assist administrators in tracking down and preventing distributed DoS attacks. </td></tr></table>
</td></tr></tbody></table></div><h6>Table 1.1. Common Exploits</h6></div><br class="table-break"/></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Threats_to_Workstation_and_Home_PC_Security-Vulnerable_Client_Applications.html"><strong>Prev</strong>1.3.4.2. Vulnerable Client Applications</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Security_Updates.html"><strong>Next</strong>1.5. Security Updates</a></li></ul></body></html>
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ommon_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Usage_Instructions.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Installation-Instructions">3.8.2. Step-by-Step Installation Instructions</h3></div></div></div><div class="itemizedlist"><ul><li><div class="para">
Open a Terminal: <code class="code">Click ''Applications'' -> ''System Tools'' -> ''Terminal''</code>
</div></li><li><div class="para">
Install 7-Zip with sudo access: <code class="code">sudo yum install p7zip</code>
</div></li><li><div class="para">
Close the Terminal: <code class="code">exit</code>
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g src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Usage_Instructions.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="chap-Security_Guide-General_Principles_of_Information_Security.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Things_of_note">3.8.4. Things of note</h3></div></div></div><div class="para">
7-Zip is not shipped by default with Microsoft Windows or Mac OS X. If you need to use your 7-Zip files on those platforms you will need to install the appropriate version of 7-Zip on those computers. See the 7-Zip <a href="http://www.7-zip.org/download.html">download page</a>.
</div><div class="para">
GNOME's File Roller application will recognize your .7z files and attempt to open them, but it will fail with the error "''An error occurred while loading the archive.''" when it attempts to do so. This is because File Roller does not currently support the extraction of encrypted 7-Zip files. A bug report ([http://bugzilla.gnome.org/show_bug.cgi?id=490732 Gnome Bug 490732]) has been submitted.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Usage_Instructions.html"><strong>Prev</strong>3.8.3. Step-by-Step Usage Instructions</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="chap-Security_Guide-General_Principles_of_Information_Security.html"><strong>Next</strong>Chapter 4. General Principles of Information Secu...</a></li></ul></body></html>
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g"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Installation-Instructions.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Things_of_note.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Usage_Instructions">3.8.3. Step-by-Step Usage Instructions</h3></div></div></div><div class="para">
By following these instructions you are going to compress and encrypt your "Documents" directory. Your original "Documents" directory will remain unaltered. This technique can be applied to any directory or file you have access to on the filesystem.
</div><div class="itemizedlist"><ul><li><div class="para">
Open a Terminal:<code class="code">Click ''Applications'' -> ''System Tools'' -> ''Terminal''</code>
</div></li><li><div class="para">
Compress and Encrypt: (enter a password when prompted) <code class="code">7za a -mhe=on -ms=on -p Documents.7z Documents/</code>
</div></li></ul></div><div class="para">
The "Documents" directory is now compressed and encrypted. The following instructions will move the encrypted archive somewhere new and then extract it.
</div><div class="itemizedlist"><ul><li><div class="para">
Create a new directory: <code class="code">mkdir newplace</code>
</div></li><li><div class="para">
Move the encrypted file: <code class="code">mv Documents.7z newplace</code>
</div></li><li><div class="para">
Go to the new directory: <code class="code">cd newplace</code>
</div></li><li><div class="para">
Extract the file: (enter the password when prompted) <code class="code">7za x Documents.7z</code>
</div></li></ul></div><div class="para">
The archive is now extracted into the new location. The following instructions will clean up all the prior steps and restore your computer to its previous state.
</div><div class="itemizedlist"><ul><li><div class="para">
Go up a directory: <code class="code">cd ..</code>
</div></li><li><div class="para">
Delete the test archive and test extraction: <code class="code">rm -r newplace</code>
</div></li><li><div class="para">
Close the Terminal: <code class="code">exit</code>
</div></li></ul></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Installation-Instructions.html"><strong>Prev</strong>3.8.2. Step-by-Step Installation Instructions</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Things_of_note.html"><strong>Next</strong>3.8.4. Things of note</a></li></ul></body></html>
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" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-LUKS_Disk_Encryption-Links_of_Interest.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Installation-Instructions.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives">3.8. 7-Zip Encrypted Archives</h2></div></div></div><div class="para">
<a href="http://www.7-zip.org/">7-Zip</a> is a cross-platform, next generation, file compression tool that can also use strong encryption (AES-256) to protect the contents of the archive. This is extremely useful when you need to move data between multiple computers that use varying operating systems (i.e. Linux at home, Windows at work) and you want a portable encryption solution.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Installation">3.8.1. 7-Zip Installation in Fedora</h3></div></div></div><div class="para">
7-Zip is not a base package in Fedora, but it is available in the software repository. Once installed, the package will update alongside the rest of the software on the computer with no special attention necessary.
</div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-LUKS_Disk_Encryption-Links_of_Interest.html"><strong>Prev</strong>3.7.5. Links of Interest</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives-Installation-Instructions.html"><strong>Next</strong>3.8.2. Step-by-Step Installation Instructions</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>3.2. Full Disk Encryption</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="chap-Security_Guide-Encryption.html" title="Chapter 3. Encryption"/><link rel="prev" href="chap-Security_Guide-Encryption.html" title="Chapter 3. Encryption"/><link rel="next" href="Security_Guide-Encryption-Protecting_Data_at_Rest-File_Based_Encryption.html" title="3.3. File Based Encryption"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li clas
s="previous"><a accesskey="p" href="chap-Security_Guide-Encryption.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="Security_Guide-Encryption-Protecting_Data_at_Rest-File_Based_Encryption.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-Encryption-Protecting_Data_at_Rest-Full_Disk_Encryption">3.2. Full Disk Encryption</h2></div></div></div><div class="para">
Full disk or partition encryption is one of the best ways of protecting your data. Not only is each file protected but also the temporary storage that may contain parts of these files is also protected. Full disk encryption will protect all of your files so you don't have to worry about selecting what you want to protect and possibly missing a file.
</div><div class="para">
Fedora 9 natively supports LUKS Encryption. LUKS will bulk encrypt your hard drive partitions so that while your computer is off your data is protected. This will also protect your computer from attackers attempting to use single-user-mode to login to your computer or otherwise gain access. LUKS can be manually setup on Fedora 8.
</div><div class="para">
Full disk encryption solutions like LUKS only protect the data when your computer is off. Once the computer is on and LUKS has decrypted the disk, the files on that disk are available to anyone who would normally have access to them. To protect your files when the computer is on, use full disk encryption in combination with another solution such as file based encryption. Also remember to lock your computer whenever you are away from it. A passphrase protected screen saver set to activate after a few minutes of inactivity is a good way to keep intruders out.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="chap-Security_Guide-Encryption.html"><strong>Prev</strong>Chapter 3. Encryption</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="Security_Guide-Encryption-Protecting_Data_at_Rest-File_Based_Encryption.html"><strong>Next</strong>3.3. File Based Encryption</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>1.2.3.5. Anticipating Your Future Needs</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Vulnerability_Assessment-Evaluating_the_Tools.html" title="1.2.3. Evaluating the Tools"/><link rel="prev" href="sect-Security_Guide-Evaluating_the_Tools-VLAD_the_Scanner.html" title="1.2.3.4. VLAD the Scanner"/><link rel="next" href="sect-Security_Guide-Attackers_and_Vulnerabilities.html" title="1.3. Attackers and Vulnerabilities"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_ri
ght.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Evaluating_the_Tools-VLAD_the_Scanner.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Attackers_and_Vulnerabilities.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Evaluating_the_Tools-Anticipating_Your_Future_Needs">1.2.3.5. Anticipating Your Future Needs</h4></div></div></div><div class="para">
Depending upon your target and resources, there are many tools available. There are tools for wireless networks, Novell networks, Windows systems, Linux systems, and more. Another essential part of performing assessments may include reviewing physical security, personnel screening, or voice/PBX network assessment. New concepts, such as <em class="firstterm">war walking</em> scanning the perimeter of your enterprise's physical structures for wireless network vulnerabilities are some emerging concepts that you can investigate and, if needed, incorporate into your assessments. Imagination and exposure are the only limits of planning and conducting vulnerability assessments.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Evaluating_the_Tools-VLAD_the_Scanner.html"><strong>Prev</strong>1.2.3.4. VLAD the Scanner</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Attackers_and_Vulnerabilities.html"><strong>Next</strong>1.3. Attackers and Vulnerabilities</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>1.2.3.2. Nessus</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Vulnerability_Assessment-Evaluating_the_Tools.html" title="1.2.3. Evaluating the Tools"/><link rel="prev" href="sect-Security_Guide-Vulnerability_Assessment-Evaluating_the_Tools.html" title="1.2.3. Evaluating the Tools"/><link rel="next" href="sect-Security_Guide-Evaluating_the_Tools-Nikto.html" title="1.2.3.3. Nikto"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></
a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Vulnerability_Assessment-Evaluating_the_Tools.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Evaluating_the_Tools-Nikto.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Evaluating_the_Tools-Nessus">1.2.3.2. Nessus</h4></div></div></div><a id="d0e847" class="indexterm"/><a id="d0e852" class="indexterm"/><div class="para">
Nessus is a full-service security scanner. The plug-in architecture of Nessus allows users to customize it for their systems and networks. As with any scanner, Nessus is only as good as the signature database it relies upon. Fortunately, Nessus is frequently updated and features full reporting, host scanning, and real-time vulnerability searches. Remember that there could be false positives and false negatives, even in a tool as powerful and as frequently updated as Nessus.
</div><div class="note"><h2>Note</h2><div class="para">
Nessus is not included with Fedora and is not supported. It has been included in this document as a reference to users who may be interested in using this popular application.
</div></div><div class="para">
For more information about Nessus, refer to the official website at the following URL:
</div><div class="para">
<a href="http://www.nessus.org/">http://www.nessus.org/</a>
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Vulnerability_Assessment-Evaluating_the_Tools.html"><strong>Prev</strong>1.2.3. Evaluating the Tools</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Evaluating_the_Tools-Nikto.html"><strong>Next</strong>1.2.3.3. Nikto</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>1.2.3.3. Nikto</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Vulnerability_Assessment-Evaluating_the_Tools.html" title="1.2.3. Evaluating the Tools"/><link rel="prev" href="sect-Security_Guide-Evaluating_the_Tools-Nessus.html" title="1.2.3.2. Nessus"/><link rel="next" href="sect-Security_Guide-Evaluating_the_Tools-VLAD_the_Scanner.html" title="1.2.3.4. VLAD the Scanner"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul
class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Evaluating_the_Tools-Nessus.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Evaluating_the_Tools-VLAD_the_Scanner.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Evaluating_the_Tools-Nikto">1.2.3.3. Nikto</h4></div></div></div><a id="d0e872" class="indexterm"/><a id="d0e877" class="indexterm"/><div class="para">
Nikto is an excellent common gateway interface (CGI) script scanner. Nikto not only checks for CGI vulnerabilities but does so in an evasive manner, so as to elude intrusion detection systems. It comes with thorough documentation which should be carefully reviewed prior to running the program. If you have Web servers serving up CGI scripts, Nikto can be an excellent resource for checking the security of these servers.
</div><div class="note"><h2>Note</h2><div class="para">
Nikto is not included with Fedora and is not supported. It has been included in this document as a reference to users who may be interested in using this popular application.
</div></div><div class="para">
More information about Nikto can be found at the following URL:
</div><div class="para">
<a href="http://www.cirt.net/code/nikto.shtml">http://www.cirt.net/code/nikto.shtml</a>
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Evaluating_the_Tools-Nessus.html"><strong>Prev</strong>1.2.3.2. Nessus</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Evaluating_the_Tools-VLAD_the_Scanner.html"><strong>Next</strong>1.2.3.4. VLAD the Scanner</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>1.2.3.4. VLAD the Scanner</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Vulnerability_Assessment-Evaluating_the_Tools.html" title="1.2.3. Evaluating the Tools"/><link rel="prev" href="sect-Security_Guide-Evaluating_the_Tools-Nikto.html" title="1.2.3.3. Nikto"/><link rel="next" href="sect-Security_Guide-Evaluating_the_Tools-Anticipating_Your_Future_Needs.html" title="1.2.3.5. Anticipating Your Future Needs"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png"
alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Evaluating_the_Tools-Nikto.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Evaluating_the_Tools-Anticipating_Your_Future_Needs.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Evaluating_the_Tools-VLAD_the_Scanner">1.2.3.4. VLAD the Scanner</h4></div></div></div><a id="d0e897" class="indexterm"/><a id="d0e902" class="indexterm"/><div class="para">
VLAD is a vulnerabilities scanner developed by the <acronym class="acronym">RAZOR</acronym> team at Bindview, Inc., which checks for the SANS Top Ten list of common security issues (SNMP issues, file sharing issues, etc.). While not as full-featured as Nessus, VLAD is worth investigating.
</div><div class="note"><h2>Note</h2><div class="para">
VLAD is not included with Fedora and is not supported. It has been included in this document as a reference to users who may be interested in using this popular application.
</div></div><div class="para">
More information about VLAD can be found on the RAZOR team website at the following URL:
</div><div class="para">
<a href="http://www.bindview.com/Support/Razor/Utilities/">http://www.bindview.com/Support/Razor/Utilities/</a>
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Evaluating_the_Tools-Nikto.html"><strong>Prev</strong>1.2.3.3. Nikto</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Evaluating_the_Tools-Anticipating_Your_Future_Needs.html"><strong>Next</strong>1.2.3.5. Anticipating Your Future Needs</a></li></ul></body></html>
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_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-FORWARD_and_NAT_Rules-Prerouting.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Firewalls-Malicious_Software_and_Spoofed_IP_Addresses.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-FORWARD_and_NAT_Rules-DMZs_and_IPTables">2.8.5.3. DMZs and IPTables</h4></div></div></div><a id="d0e13629" class="indexterm"/><a id="d0e13635" class="indexterm"/><a id="d0e13640" class="indexterm"/><a id="d0e13643" class="indexterm"/><a id="d0e13651" class="indexterm"/><div class="para">
You can create <code class="command">iptables</code> rules to route traffic to certain machines, such as a dedicated HTTP or FTP server, in a <em class="firstterm">demilitarized zone</em> (<acronym class="acronym">DMZ</acronym>). A <acronym class="acronym">DMZ</acronym> is a special local subnetwork dedicated to providing services on a public carrier, such as the Internet.
</div><div class="para">
For example, to set a rule for routing incoming HTTP requests to a dedicated HTTP server at 10.0.4.2 (outside of the 192.168.1.0/24 range of the LAN), NAT uses the <code class="computeroutput">PREROUTING</code> table to forward the packets to the appropriate destination:
</div><pre class="screen">[root@myServer ~ ] # iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j DNAT --to-destination 10.0.4.2:80
</pre><div class="para">
With this command, all HTTP connections to port 80 from outside of the LAN are routed to the HTTP server on a network separate from the rest of the internal network. This form of network segmentation can prove safer than allowing HTTP connections to a machine on the network.
</div><div class="para">
If the HTTP server is configured to accept secure connections, then port 443 must be forwarded as well.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-FORWARD_and_NAT_Rules-Prerouting.html"><strong>Prev</strong>2.8.5.2. Prerouting</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Firewalls-Malicious_Software_and_Spoofed_IP_Addresses.html"><strong>Next</strong>2.8.6. Malicious Software and Spoofed IP Addresses</a></li></ul></body></html>
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></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Firewalls-FORWARD_and_NAT_Rules.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-FORWARD_and_NAT_Rules-DMZs_and_IPTables.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-FORWARD_and_NAT_Rules-Prerouting">2.8.5.2. Prerouting</h4></div></div></div><a id="d0e13595" class="indexterm"/><div class="para">
If you have a server on your internal network that you want make available externally, you can use the <code class="option">-j DNAT</code> target of the PREROUTING chain in NAT to specify a destination IP address and port where incoming packets requesting a connection to your internal service can be forwarded.
</div><div class="para">
For example, if you want to forward incoming HTTP requests to your dedicated Apache HTTP Server at 172.31.0.23, use the following command:
</div><pre class="screen">[root@myServer ~ ] # iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j DNAT --to 172.31.0.23:80
</pre><div class="para">
This rule specifies that the <acronym class="acronym">nat</acronym> table use the built-in PREROUTING chain to forward incoming HTTP requests exclusively to the listed destination IP address of 172.31.0.23.
</div><div class="note"><h2>Note</h2><div class="para">
If you have a default policy of DROP in your FORWARD chain, you must append a rule to forward all incoming HTTP requests so that destination NAT routing is possible. To do this, use the following command:
</div><pre class="screen">[root@myServer ~ ] # iptables -A FORWARD -i eth0 -p tcp --dport 80 -d 172.31.0.23 -j ACCEPT
</pre><div class="para">
This rule forwards all incoming HTTP requests from the firewall to the intended destination; the Apache HTTP Server behind the firewall.
</div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Firewalls-FORWARD_and_NAT_Rules.html"><strong>Prev</strong>2.8.5. FORWARD and NAT Rules</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-FORWARD_and_NAT_Rules-DMZs_and_IPTables.html"><strong>Next</strong>2.8.5.3. DMZs and IPTables</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.8.9. Additional Resources</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Firewalls.html" title="2.8. Firewalls"/><link rel="prev" href="sect-Security_Guide-Firewalls-IPv6.html" title="2.8.8. IPv6"/><link rel="next" href="sect-Security_Guide-Additional_Resources-Useful_Firewall_Websites.html" title="2.8.9.2. Useful Firewall Websites"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous">
<a accesskey="p" href="sect-Security_Guide-Firewalls-IPv6.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Additional_Resources-Useful_Firewall_Websites.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Firewalls-Additional_Resources">2.8.9. Additional Resources</h3></div></div></div><a id="d0e13868" class="indexterm"/><a id="d0e13873" class="indexterm"/><a id="d0e13878" class="indexterm"/><div class="para">
There are several aspects to firewalls and the Linux Netfilter subsystem that could not be covered in this chapter. For more information, refer to the following resources.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Additional_Resources-Installed_Firewall_Documentation">2.8.9.1. Installed Firewall Documentation</h4></div></div></div><div class="itemizedlist"><ul><li><div class="para">
Refer to <a class="xref" href="sect-Security_Guide-IPTables.html" title="2.9. IPTables">Section 2.9, “IPTables”</a> for more detailed information on the <code class="command">iptables</code> command, including definitions for many command options.
</div></li><li><div class="para">
The <code class="command">iptables</code> man page contains a brief summary of the various options.
</div></li></ul></div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Firewalls-IPv6.html"><strong>Prev</strong>2.8.8. IPv6</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Additional_Resources-Useful_Firewall_Websites.html"><strong>Next</strong>2.8.9.2. Useful Firewall Websites</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.8.2. Basic Firewall Configuration</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Firewalls.html" title="2.8. Firewalls"/><link rel="prev" href="sect-Security_Guide-Firewalls.html" title="2.8. Firewalls"/><link rel="next" href="sect-Security_Guide-Basic_Firewall_Configuration-Enabling_and_Disabling_the_Firewall.html" title="2.8.2.2. Enabling and Disabling the Firewall"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul
class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Firewalls.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Basic_Firewall_Configuration-Enabling_and_Disabling_the_Firewall.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Firewalls-Basic_Firewall_Configuration">2.8.2. Basic Firewall Configuration</h3></div></div></div><a id="d0e12871" class="indexterm"/><div class="para">
Just as a firewall in a building attempts to prevent a fire from spreading, a computer firewall attempts to prevent malicious software from spreading to your computer. It also helps to prevent unauthorized users from accessing your computer.
</div><div class="para">
In a default Fedora installation, a firewall exists between your computer or network and any untrusted networks, for example the Internet. It determines which services on your computer remote users can access. A properly configured firewall can greatly increase the security of your system. It is recommended that you configure a firewall for any Fedora system with an Internet connection.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Basic_Firewall_Configuration-RHSECLEVELTOOL">2.8.2.1. <span class="application"><strong>Security Level Configuration Tool</strong></span></h4></div></div></div><a id="d0e12885" class="indexterm"/><a id="d0e12891" class="indexterm"/><div class="para">
During the <span class="guilabel"><strong>Firewall Configuration</strong></span> screen of the Fedora installation, you were given the option to enable a basic firewall as well as to allow specific devices, incoming services, and ports.
</div><div class="para">
After installation, you can change this preference by using the <span class="application"><strong>Security Level Configuration Tool</strong></span>.
</div><div class="para">
To start this application, use the following command:
</div><pre class="screen">[root@myServer ~] # system-config-securitylevel
</pre><div class="figure" id="figu-Security_Guide-RHSECLEVELTOOL-RHSECLEVELTOOL"><div class="figure-contents"><div class="mediaobject"><img src="images/rh-securitylevel.png" alt="Security Level Configuration Tool"/><div class="longdesc"><div class="para">
Security Level Configuration
</div></div></div></div><h6>Figure 2.15. <span class="application">Security Level Configuration Tool</span></h6></div><br class="figure-break"/><div class="note"><h2>Note</h2><div class="para">
The <span class="application"><strong>Security Level Configuration Tool</strong></span> only configures a basic firewall. If the system needs more complex rules, refer to <a class="xref" href="sect-Security_Guide-IPTables.html" title="2.9. IPTables">Section 2.9, “IPTables”</a> for details on configuring specific <code class="command">iptables</code> rules.
</div></div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Firewalls.html"><strong>Prev</strong>2.8. Firewalls</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Basic_Firewall_Configuration-Enabling_and_Disabling_the_Firewall.html"><strong>Next</strong>2.8.2.2. Enabling and Disabling the Firewall</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.8.4. Common IPTables Filtering</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Firewalls.html" title="2.8. Firewalls"/><link rel="prev" href="sect-Security_Guide-Using_IPTables-Saving_and_Restoring_IPTables_Rules.html" title="2.8.3.3. Saving and Restoring IPTables Rules"/><link rel="next" href="sect-Security_Guide-Firewalls-FORWARD_and_NAT_Rules.html" title="2.8.5. FORWARD and NAT Rules"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation
Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Using_IPTables-Saving_and_Restoring_IPTables_Rules.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Firewalls-FORWARD_and_NAT_Rules.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Firewalls-Common_IPTables_Filtering">2.8.4. Common IPTables Filtering</h3></div></div></div><a id="d0e13368" class="indexterm"/><a id="d0e13376" class="indexterm"/><a id="d0e13384" class="indexterm"/><div class="para">
Preventing remote attackers from accessing a LAN is one of the most important aspects of network security. The integrity of a LAN should be protected from malicious remote users through the use of stringent firewall rules.
</div><div class="para">
However, with a default policy set to block all incoming, outgoing, and forwarded packets, it is impossible for the firewall/gateway and internal LAN users to communicate with each other or with external resources.
</div><div class="para">
To allow users to perform network-related functions and to use networking applications, administrators must open certain ports for communication.
</div><div class="para">
For example, to allow access to port 80 <span class="emphasis"><em>on the firewall</em></span>, append the following rule:
</div><pre class="screen">[root@myServer ~ ] # iptables -A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
</pre><div class="para">
This allows users to browse websites that communicate using the standard port 80. To allow access to secure websites (for example, https://www.example.com/), you also need to provide access to port 443, as follows:
</div><pre class="screen">[root@myServer ~ ] # iptables -A INPUT -p tcp -m tcp --dport 443 -j ACCEPT
</pre><div class="important"><h2>Important</h2><div class="para">
When creating an <code class="command">iptables</code> ruleset, order is important.
</div><div class="para">
If a rule specifies that any packets from the 192.168.100.0/24 subnet be dropped, and this is followed by a rule that allows packets from 192.168.100.13 (which is within the dropped subnet), then the second rule is ignored.
</div><div class="para">
The rule to allow packets from 192.168.100.13 must precede the rule that drops the remainder of the subnet.
</div><div class="para">
To insert a rule in a specific location in an existing chain, use the <code class="option">-I</code> option. For example:
</div><pre class="screen">[root@myServer ~ ] # iptables -I INPUT 1 -i lo -p all -j ACCEPT
</pre><div class="para">
This rule is inserted as the first rule in the INPUT chain to allow local loopback device traffic.
</div></div><div class="para">
There may be times when you require remote access to the LAN. Secure services, for example SSH, can be used for encrypted remote connection to LAN services.
</div><div class="para">
Administrators with PPP-based resources (such as modem banks or bulk ISP accounts), dial-up access can be used to securely circumvent firewall barriers. Because they are direct connections, modem connections are typically behind a firewall/gateway.
</div><div class="para">
For remote users with broadband connections, however, special cases can be made. You can configure <code class="command">iptables</code> to accept connections from remote SSH clients. For example, the following rules allow remote SSH access:
</div><pre class="screen">[root@myServer ~ ] # iptables -A INPUT -p tcp --dport 22 -j ACCEPT
[root@myServer ~ ] # iptables -A OUTPUT -p tcp --sport 22 -j ACCEPT
</pre><div class="para">
These rules allow incoming and outbound access for an individual system, such as a single PC directly connected to the Internet or a firewall/gateway. However, they do not allow nodes behind the firewall/gateway to access these services. To allow LAN access to these services, you can use <em class="firstterm">Network Address Translation</em> (<acronym class="acronym">NAT</acronym>) with <code class="command">iptables</code> filtering rules.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Using_IPTables-Saving_and_Restoring_IPTables_Rules.html"><strong>Prev</strong>2.8.3.3. Saving and Restoring IPTables Rules</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Firewalls-FORWARD_and_NAT_Rules.html"><strong>Next</strong>2.8.5. FORWARD and NAT Rules</a></li></ul></body></html>
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lass="previous"><a accesskey="p" href="sect-Security_Guide-Firewalls-Common_IPTables_Filtering.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-FORWARD_and_NAT_Rules-Prerouting.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Firewalls-FORWARD_and_NAT_Rules">2.8.5. <code class="computeroutput">FORWARD</code> and <acronym class="acronym">NAT</acronym> Rules</h3></div></div></div><a id="d0e13460" class="indexterm"/><a id="d0e13465" class="indexterm"/><a id="d0e13468" class="indexterm"/><a id="d0e13475" class="indexterm"/><a id="d0e13483" class="indexterm"/><div class="para">
Most ISPs provide only a limited number of publicly routable IP addresses to the organizations they serve.
</div><div class="para">
Administrators must, therefore, find alternative ways to share access to Internet services without giving public IP addresses to every node on the LAN. Using private IP addresses is the most common way of allowing all nodes on a LAN to properly access internal and external network services.
</div><div class="para">
Edge routers (such as firewalls) can receive incoming transmissions from the Internet and route the packets to the intended LAN node. At the same time, firewalls/gateways can also route outgoing requests from a LAN node to the remote Internet service.
</div><div class="para">
This forwarding of network traffic can become dangerous at times, especially with the availability of modern cracking tools that can spoof <span class="emphasis"><em>internal</em></span> IP addresses and make the remote attacker's machine act as a node on your LAN.
</div><div class="para">
To prevent this, <code class="command">iptables</code> provides routing and forwarding policies that can be implemented to prevent abnormal usage of network resources.
</div><div class="para">
The <code class="computeroutput">FORWARD</code> chain allows an administrator to control where packets can be routed within a LAN. For example, to allow forwarding for the entire LAN (assuming the firewall/gateway is assigned an internal IP address on eth1), use the following rules:
</div><pre class="screen">[root@myServer ~ ] # iptables -A FORWARD -i eth1 -j ACCEPT
[root@myServer ~ ] # iptables -A FORWARD -o eth1 -j ACCEPT
</pre><div class="para">
This rule gives systems behind the firewall/gateway access to the internal network. The gateway routes packets from one LAN node to its intended destination node, passing all packets through its <code class="filename">eth1</code> device.
</div><div class="note"><h2>Note</h2><div class="para">
By default, the IPv4 policy in Fedora kernels disables support for IP forwarding. This prevents machines that run Fedora from functioning as dedicated edge routers. To enable IP forwarding, use the following command:
</div><pre class="screen">[root@myServer ~ ] # sysctl -w net.ipv4.ip_forward=1
</pre><div class="para">
This configuration change is only valid for the current session; it does not persist beyond a reboot or network service restart. To permanently set IP forwarding, edit the <code class="filename">/etc/sysctl.conf</code> file as follows:
</div><div class="para">
Locate the following line:
</div><pre class="screen">net.ipv4.ip_forward = 0
</pre><div class="para">
Edit it to read as follows:
</div><pre class="screen">net.ipv4.ip_forward = 1
</pre><div class="para">
Use the following command to enable the change to the <code class="filename">sysctl.conf</code> file:
</div><pre class="screen">[root@myServer ~ ] # sysctl -p /etc/sysctl.conf
</pre></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-FORWARD_and_NAT_Rules-Postrouting_and_IP_Masquerading">2.8.5.1. Postrouting and IP Masquerading</h4></div></div></div><a id="d0e13549" class="indexterm"/><a id="d0e13557" class="indexterm"/><div class="para">
Accepting forwarded packets via the firewall's internal IP device allows LAN nodes to communicate with each other; however they still cannot communicate externally to the Internet.
</div><div class="para">
To allow LAN nodes with private IP addresses to communicate with external public networks, configure the firewall for <em class="firstterm">IP masquerading</em>, which masks requests from LAN nodes with the IP address of the firewall's external device (in this case, eth0):
</div><pre class="screen">[root@myServer ~ ] # iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
</pre><div class="para">
This rule uses the NAT packet matching table (<code class="option">-t nat</code>) and specifies the built-in POSTROUTING chain for NAT (<code class="option">-A POSTROUTING</code>) on the firewall's external networking device (<code class="option">-o eth0</code>).
</div><div class="para">
POSTROUTING allows packets to be altered as they are leaving the firewall's external device.
</div><div class="para">
The <code class="option">-j MASQUERADE</code> target is specified to mask the private IP address of a node with the external IP address of the firewall/gateway.
</div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Firewalls-Common_IPTables_Filtering.html"><strong>Prev</strong>2.8.4. Common IPTables Filtering</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-FORWARD_and_NAT_Rules-Prerouting.html"><strong>Next</strong>2.8.5.2. Prerouting</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.8.7. IPTables and Connection Tracking</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Firewalls.html" title="2.8. Firewalls"/><link rel="prev" href="sect-Security_Guide-Firewalls-Malicious_Software_and_Spoofed_IP_Addresses.html" title="2.8.6. Malicious Software and Spoofed IP Addresses"/><link rel="next" href="sect-Security_Guide-Firewalls-IPv6.html" title="2.8.8. IPv6"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul
class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Firewalls-Malicious_Software_and_Spoofed_IP_Addresses.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Firewalls-IPv6.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Firewalls-IPTables_and_Connection_Tracking">2.8.7. IPTables and Connection Tracking</h3></div></div></div><a id="d0e13752" class="indexterm"/><a id="d0e13757" class="indexterm"/><a id="d0e13762" class="indexterm"/><a id="d0e13768" class="indexterm"/><div class="para">
You can inspect and restrict connections to services based on their <em class="firstterm">connection state.</em> A module within <code class="command">iptables</code> uses a method called <em class="firstterm">connection tracking</em> to store information about incoming connections. You can allow or deny access based on the following connection states:
</div><a id="d0e13785" class="indexterm"/><a id="d0e13793" class="indexterm"/><div class="itemizedlist"><ul><li><div class="para">
<code class="option">NEW</code> — A packet requesting a new connection, such as an HTTP request.
</div></li><li><div class="para">
<code class="option">ESTABLISHED</code> — A packet that is part of an existing connection.
</div></li><li><div class="para">
<code class="option">RELATED</code> — A packet that is requesting a new connection but is part of an existing connection. For example, FTP uses port 21 to establish a connection, but data is transferred on a different port (typically port 20).
</div></li><li><div class="para">
<code class="option">INVALID</code> — A packet that is not part of any connections in the connection tracking table.
</div></li></ul></div><div class="para">
You can use the stateful functionality of <code class="command">iptables</code> connection tracking with any network protocol, even if the protocol itself is stateless (such as UDP). The following example shows a rule that uses connection tracking to forward only the packets that are associated with an established connection:
</div><pre class="screen">[root@myServer ~ ] # iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT
</pre></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Firewalls-Malicious_Software_and_Spoofed_IP_Addresses.html"><strong>Prev</strong>2.8.6. Malicious Software and Spoofed IP Addresses</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Firewalls-IPv6.html"><strong>Next</strong>2.8.8. IPv6</a></li></ul></body></html>
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i class="previous"><a accesskey="p" href="sect-Security_Guide-Firewalls-IPTables_and_Connection_Tracking.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Firewalls-Additional_Resources.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Firewalls-IPv6">2.8.8. IPv6</h3></div></div></div><a id="d0e13836" class="indexterm"/><a id="d0e13840" class="indexterm"/><div class="para">
The introduction of the next-generation Internet Protocol, called IPv6, expands beyond the 32-bit address limit of IPv4 (or IP). IPv6 supports 128-bit addresses, and carrier networks that are IPv6 aware are therefore able to address a larger number of routable addresses than IPv4.
</div><div class="para">
Fedora supports IPv6 firewall rules using the Netfilter 6 subsystem and the <code class="command">ip6tables</code> command. In Fedora 5, both IPv4 and IPv6 services are enabled by default.
</div><div class="para">
The <code class="command">ip6tables</code> command syntax is identical to <code class="command">iptables</code> in every aspect except that it supports 128-bit addresses. For example, use the following command to enable SSH connections on an IPv6-aware network server:
</div><pre class="screen">[root@myServer ~ ] # ip6tables -A INPUT -i eth0 -p tcp -s 3ffe:ffff:100::1/128 --dport 22 -j ACCEPT
</pre><div class="para">
For more information about IPv6 networking, refer to the IPv6 Information Page at <a href="http://www.ipv6.org/">http://www.ipv6.org/</a>.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Firewalls-IPTables_and_Connection_Tracking.html"><strong>Prev</strong>2.8.7. IPTables and Connection Tracking</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Firewalls-Additional_Resources.html"><strong>Next</strong>2.8.9. Additional Resources</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.8.6. Malicious Software and Spoofed IP Addresses</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Firewalls.html" title="2.8. Firewalls"/><link rel="prev" href="sect-Security_Guide-FORWARD_and_NAT_Rules-DMZs_and_IPTables.html" title="2.8.5.3. DMZs and IPTables"/><link rel="next" href="sect-Security_Guide-Firewalls-IPTables_and_Connection_Tracking.html" title="2.8.7. IPTables and Connection Tracking"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Doc
umentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-FORWARD_and_NAT_Rules-DMZs_and_IPTables.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Firewalls-IPTables_and_Connection_Tracking.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Firewalls-Malicious_Software_and_Spoofed_IP_Addresses">2.8.6. Malicious Software and Spoofed IP Addresses</h3></div></div></div><a id="d0e13687" class="indexterm"/><a id="d0e13692" class="indexterm"/><div class="para">
More elaborate rules can be created that control access to specific subnets, or even specific nodes, within a LAN. You can also restrict certain dubious applications or programs such as trojans, worms, and other client/server viruses from contacting their server.
</div><div class="para">
For example, some trojans scan networks for services on ports from 31337 to 31340 (called the <span class="emphasis"><em>elite</em></span> ports in cracking terminology).
</div><div class="para">
Since there are no legitimate services that communicate via these non-standard ports, blocking them can effectively diminish the chances that potentially infected nodes on your network independently communicate with their remote master servers.
</div><div class="para">
The following rules drop all TCP traffic that attempts to use port 31337:
</div><pre class="screen">[root@myServer ~ ] # iptables -A OUTPUT -o eth0 -p tcp --dport 31337 --sport 31337 -j DROP
[root@myServer ~ ] # iptables -A FORWARD -o eth0 -p tcp --dport 31337 --sport 31337 -j DROP
</pre><div class="para">
You can also block outside connections that attempt to spoof private IP address ranges to infiltrate your LAN.
</div><div class="para">
For example, if your LAN uses the 192.168.1.0/24 range, you can design a rule that instructs the Internet-facing network device (for example, eth0) to drop any packets to that device with an address in your LAN IP range.
</div><div class="para">
Because it is recommended to reject forwarded packets as a default policy, any other spoofed IP address to the external-facing device (eth0) is rejected automatically.
</div><pre class="screen">[root@myServer ~ ] # iptables -A FORWARD -s 192.168.1.0/24 -i eth0 -j DROP
</pre><div class="note"><h2>Note</h2><div class="para">
There is a distinction between the <code class="computeroutput">DROP</code> and <code class="computeroutput">REJECT</code> targets when dealing with <span class="emphasis"><em>appended</em></span> rules.
</div><div class="para">
The <code class="computeroutput">REJECT</code> target denies access and returns a <code class="computeroutput">connection refused</code> error to users who attempt to connect to the service. The <code class="computeroutput">DROP</code> target, as the name implies, drops the packet without any warning.
</div><div class="para">
Administrators can use their own discretion when using these targets. However, to avoid user confusion and attempts to continue connecting, the <code class="computeroutput">REJECT</code> target is recommended.
</div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-FORWARD_and_NAT_Rules-DMZs_and_IPTables.html"><strong>Prev</strong>2.8.5.3. DMZs and IPTables</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Firewalls-IPTables_and_Connection_Tracking.html"><strong>Next</strong>2.8.7. IPTables and Connection Tracking</a></li></ul></body></html>
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ation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Basic_Firewall_Configuration-Activating_the_IPTables_Service.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Using_IPTables-Basic_Firewall_Policies.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Firewalls-Using_IPTables">2.8.3. Using IPTables</h3></div></div></div><a id="d0e13191" class="indexterm"/><div class="para">
The first step in using <code class="command">iptables</code> is to start the <code class="command">iptables</code> service. Use the following command to start the <code class="command">iptables</code> service:
</div><pre class="screen">[root@myServer ~] # service iptables start
</pre><div class="note"><h2>Note</h2><div class="para">
The <code class="command">ip6tables</code> service can be turned off if you intend to use the <code class="command">iptables</code> service only. If you deactivate the <code class="command">ip6tables</code> service, remember to deactivate the IPv6 network also. Never leave a network device active without the matching firewall.
</div></div><div class="para">
To force <code class="command">iptables</code> to start by default when the system is booted, use the following command:
</div><pre class="screen">[root@myServer ~] # chkconfig --level 345 iptables on
</pre><div class="para">
This forces <code class="command">iptables</code> to start whenever the system is booted into runlevel 3, 4, or 5.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Using_IPTables-IPTables_Command_Syntax">2.8.3.1. IPTables Command Syntax</h4></div></div></div><div class="para">
The following sample <code class="command">iptables</code> command illustrates the basic command syntax:
</div><pre class="screen">[root@myServer ~ ] # iptables -A <em class="replaceable"><code><chain></code></em> -j <em class="replaceable"><code><target></code></em>
</pre><a id="d0e13252" class="indexterm"/><div class="para">
The <code class="option">-A</code> option specifies that the rule be appended to <em class="firstterm"><chain></em>. Each chain is comprised of one or more <em class="firstterm">rules</em>, and is therefore also known as a <em class="firstterm">ruleset</em>.
</div><div class="para">
The three built-in chains are INPUT, OUTPUT, and FORWARD. These chains are permanent and cannot be deleted. The chain specifies the point at which a packet is manipulated.
</div><div class="para">
The <code class="option">-j <em class="replaceable"><code><target></code></em></code> option specifies the target of the rule; i.e., what to do if the packet matches the rule. Examples of built-in targets are ACCEPT, DROP, and REJECT.
</div><div class="para">
Refer to the <code class="command">iptables</code> man page for more information on the available chains, options, and targets.
</div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Basic_Firewall_Configuration-Activating_the_IPTables_Service.html"><strong>Prev</strong>2.8.2.6. Activating the IPTables Service</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Using_IPTables-Basic_Firewall_Policies.html"><strong>Next</strong>2.8.3.2. Basic Firewall Policies</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.8. Firewalls</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="chap-Security_Guide-Securing_Your_Network.html" title="Chapter 2. Securing Your Network"/><link rel="prev" href="sect-Security_Guide-Virtual_Private_Networks_VPNs-Starting_and_Stopping_an_IPsec_Connection.html" title="2.7.8. Starting and Stopping an IPsec Connection"/><link rel="next" href="sect-Security_Guide-Firewalls-Basic_Firewall_Configuration.html" title="2.8.2. Basic Firewall Configuration"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common
_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Virtual_Private_Networks_VPNs-Starting_and_Stopping_an_IPsec_Connection.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Firewalls-Basic_Firewall_Configuration.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-Firewalls">2.8. Firewalls</h2></div></div></div><a id="d0e12677" class="indexterm"/><div class="para">
Information security is commonly thought of as a process and not a product. However, standard security implementations usually employ some form of dedicated mechanism to control access privileges and restrict network resources to users who are authorized, identifiable, and traceable. Fedora includes several tools to assist administrators and security engineers with network-level access control issues.
</div><div class="para">
Firewalls are one of the core components of a network security implementation. Several vendors market firewall solutions catering to all levels of the marketplace: from home users protecting one PC to data center solutions safeguarding vital enterprise information. Firewalls can be stand-alone hardware solutions, such as firewall appliances by Cisco, Nokia, and Sonicwall. Vendors such as Checkpoint, McAfee, and Symantec have also developed proprietary software firewall solutions for home and business markets.
</div><div class="para">
Apart from the differences between hardware and software firewalls, there are also differences in the way firewalls function that separate one solution from another. <a class="xref" href="sect-Security_Guide-Firewalls.html#tabl-Security_Guide-Firewalls-Firewall_Types" title="Table 2.2. Firewall Types">Table 2.2, “Firewall Types”</a> details three common types of firewalls and how they function:
</div><a id="d0e12688" class="indexterm"/><a id="d0e12693" class="indexterm"/><a id="d0e12696" class="indexterm"/><a id="d0e12701" class="indexterm"/><a id="d0e12706" class="indexterm"/><div class="table" id="tabl-Security_Guide-Firewalls-Firewall_Types"><div class="table-contents"><table summary="Firewall Types" border="1"><colgroup><col width="1*"/><col width="3*"/><col width="3*"/><col width="3*"/></colgroup><thead><tr><th>
Method
</th><th>
Description
</th><th>
Advantages
</th><th>
Disadvantages
</th></tr></thead><tbody><tr><td>
NAT
</td><td>
<em class="firstterm">Network Address Translation</em> (NAT) places private IP subnetworks behind one or a small pool of public IP addresses, masquerading all requests to one source rather than several. The Linux kernel has built-in NAT functionality through the Netfilter kernel subsystem.
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> · Can be configured transparently to machines on a LAN </td></tr><tr><td> · Protection of many machines and services behind one or more external IP addresses simplifies administration duties </td></tr><tr><td> · Restriction of user access to and from the LAN can be configured by opening and closing ports on the NAT firewall/gateway </td></tr></table>
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> · Cannot prevent malicious activity once users connect to a service outside of the firewall </td></tr></table>
</td></tr><tr><td>
Packet Filter
</td><td>
A packet filtering firewall reads each data packet that passes through a LAN. It can read and process packets by header information and filters the packet based on sets of programmable rules implemented by the firewall administrator. The Linux kernel has built-in packet filtering functionality through the Netfilter kernel subsystem.
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> · Customizable through the <code class="command">iptables</code> front-end utility </td></tr><tr><td> · Does not require any customization on the client side, as all network activity is filtered at the router level rather than the application level </td></tr><tr><td> · Since packets are not transmitted through a proxy, network performance is faster due to direct connection from client to remote host </td></tr></table>
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> · Cannot filter packets for content like proxy firewalls </td></tr><tr><td> · Processes packets at the protocol layer, but cannot filter packets at an application layer </td></tr><tr><td> · Complex network architectures can make establishing packet filtering rules difficult, especially if coupled with <em class="firstterm">IP masquerading</em> or local subnets and DMZ networks </td></tr></table>
</td></tr><tr><td>
Proxy
</td><td>
Proxy firewalls filter all requests of a certain protocol or type from LAN clients to a proxy machine, which then makes those requests to the Internet on behalf of the local client. A proxy machine acts as a buffer between malicious remote users and the internal network client machines.
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> · Gives administrators control over what applications and protocols function outside of the LAN </td></tr><tr><td> · Some proxy servers can cache frequently-accessed data locally rather than having to use the Internet connection to request it. This helps to reduce bandwidth consumption </td></tr><tr><td> · Proxy services can be logged and monitored closely, allowing tighter control over resource utilization on the network </td></tr></table>
</td><td>
<table class="simplelist" border="0" summary="Simple list"><tr><td> · Proxies are often application-specific (HTTP, Telnet, etc.), or protocol-restricted (most proxies work with TCP-connected services only) </td></tr><tr><td> · Application services cannot run behind a proxy, so your application servers must use a separate form of network security </td></tr><tr><td> · Proxies can become a network bottleneck, as all requests and transmissions are passed through one source rather than directly from a client to a remote service </td></tr></table>
</td></tr></tbody></table></div><h6>Table 2.2. Firewall Types</h6></div><br class="table-break"/><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Firewalls-Netfilter_and_IPTables">2.8.1. Netfilter and IPTables</h3></div></div></div><a id="d0e12813" class="indexterm"/><a id="d0e12817" class="indexterm"/><a id="d0e12820" class="indexterm"/><div class="para">
The Linux kernel features a powerful networking subsystem called <em class="firstterm">Netfilter</em>. The Netfilter subsystem provides stateful or stateless packet filtering as well as NAT and IP masquerading services. Netfilter also has the ability to <em class="firstterm">mangle</em> IP header information for advanced routing and connection state management. Netfilter is controlled using the <code class="command">iptables</code> tool.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Netfilter_and_IPTables-IPTables_Overview">2.8.1.1. IPTables Overview</h4></div></div></div><div class="para">
The power and flexibility of Netfilter is implemented using the <code class="command">iptables</code> administration tool, a command line tool similar in syntax to its predecessor, <code class="command">ipchains</code>.
</div><div class="para">
A similar syntax does not mean similar implementation, however. <code class="command">ipchains</code> requires intricate rule sets for: filtering source paths; filtering destination paths; and filtering both source and destination connection ports.
</div><div class="para">
By contrast, <code class="command">iptables</code> uses the Netfilter subsystem to enhance network connection, inspection, and processing. <code class="command">iptables</code> features advanced logging, pre- and post-routing actions, network address translation, and port forwarding, all in one command line interface.
</div><div class="para">
This section provides an overview of <code class="command">iptables</code>. For more detailed information, refer to <a class="xref" href="sect-Security_Guide-IPTables.html" title="2.9. IPTables">Section 2.9, “IPTables”</a>.
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image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-General_Principles_of_Information_Security-NSA_Documents.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="chap-Security_Guide-Secure_Installation.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-General_Principles_of_Information_Security-DISA_IASE_Documents">4.4. DISA IASE Documents</h2></div></div></div><div class="itemizedlist"><ul><li><div class="para">
<a href="iase.disa.mil/stigs/stig/index.html">Security Technical Implementation Guides</a> (STIG) Scroll down to the Unix STIG
</div></li><li><div class="para">
<a href="iase.disa.mil/stigs/checklist/index.html">Security Checklists</a> Scroll down to the Unix Security Checklists
</div></li><li><div class="para">
<a href="iase.disa.mil/stigs/SRR/unix.html">Unix Security Readiness Review Evaluation Script</a>
</div></li></ul></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-General_Principles_of_Information_Security-NSA_Documents.html"><strong>Prev</strong>4.3. NSA Documents</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="chap-Security_Guide-Secure_Installation.html"><strong>Next</strong>Chapter 5. Secure Installation</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>4.3. NSA Documents</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="chap-Security_Guide-General_Principles_of_Information_Security.html" title="Chapter 4. General Principles of Information Security"/><link rel="prev" href="sect-Security_Guide-General_Principles_of_Information_Security-Tips_Guides_and_Tools.html" title="4.2. Tips, Guides, and Tools"/><link rel="next" href="sect-Security_Guide-General_Principles_of_Information_Security-DISA_IASE_Documents.html" title="4.4. DISA IASE Documents"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fed
oraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-General_Principles_of_Information_Security-Tips_Guides_and_Tools.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-General_Principles_of_Information_Security-DISA_IASE_Documents.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-General_Principles_of_Information_Security-NSA_Documents">4.3. NSA Documents</h2></div></div></div><div class="itemizedlist"><ul><li><div class="para">
<a href="www.nsa.gov/notices/notic00004.cfm?Address=/snac/os/redhat/rhel5-pamphlet...">Hardening Tips for the Red Hat Enterprise Linux 5 (PDF)</a>
</div></li><li><div class="para">
<a href="www.nsa.gov/notices/notic00004.cfm?Address=/snac/os/redhat/rhel5-guide-i7...">Guide to the Secure Configuration of Red Hat Enterprise Linux 5 (PDF)</a>
</div></li></ul></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-General_Principles_of_Information_Security-Tips_Guides_and_Tools.html"><strong>Prev</strong>4.2. Tips, Guides, and Tools</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-General_Principles_of_Information_Security-DISA_IASE_Documents.html"><strong>Next</strong>4.4. DISA IASE Documents</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>4.2. Tips, Guides, and Tools</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="chap-Security_Guide-General_Principles_of_Information_Security.html" title="Chapter 4. General Principles of Information Security"/><link rel="prev" href="chap-Security_Guide-General_Principles_of_Information_Security.html" title="Chapter 4. General Principles of Information Security"/><link rel="next" href="sect-Security_Guide-General_Principles_of_Information_Security-NSA_Documents.html" title="4.3. NSA Documents"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.f
edoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="chap-Security_Guide-General_Principles_of_Information_Security.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-General_Principles_of_Information_Security-NSA_Documents.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-General_Principles_of_Information_Security-Tips_Guides_and_Tools">4.2. Tips, Guides, and Tools</h2></div></div></div><div class="para">
Most of the above tips are very basic. Depending on your knowledge of Linux and how comfortable you are with modifying your system, some changes could be made to help make your installation more secure. As mentioned above, the NSA has hardening guides and tips for securing Red Hat Enterprise Linux 5. Likewise, the <a href="http://www.disa.mil/">Defense Information Systems Agency</a> (DISA) has an <a href="iase.disa.mil">Information Assurance Support Environment</a> in which they publish checklists and tests for verifying the security of your system. The documents from the NSA are a good read for anyone familiar with Linux while the information from DISA is extremely specific and advanced knowledge of Unix/Linux would be a great benefit. Links to these documents are listed below. We will try to pull some of the larger items out of these documents and explain how to implement them in Fedora and why they are important. In addition to documentation, DISA has made available SRR
scripts that allow an administrator to check specific settings on a system quickly. The SRR scripts will provide an XML-formatted report listing any known vulnerable settings that you have on your system.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="chap-Security_Guide-General_Principles_of_Information_Security.html"><strong>Prev</strong>Chapter 4. General Principles of Information Secu...</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-General_Principles_of_Information_Security-NSA_Documents.html"><strong>Next</strong>4.3. NSA Documents</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.9.7. Additional Resources</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-IPTables.html" title="2.9. IPTables"/><link rel="prev" href="sect-Security_Guide-IPTables-IPTables_and_IPv6.html" title="2.9.6. IPTables and IPv6"/><link rel="next" href="sect-Security_Guide-Additional_Resources-Useful_IP_Tables_Websites.html" title="2.9.7.2. Useful IP Tables Websites"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docn
av"><li class="previous"><a accesskey="p" href="sect-Security_Guide-IPTables-IPTables_and_IPv6.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Additional_Resources-Useful_IP_Tables_Websites.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-IPTables-Additional_Resources">2.9.7. Additional Resources</h3></div></div></div><a id="d0e16237" class="indexterm"/><div class="para">
Refer to the following sources for additional information on packet filtering with <code class="command">iptables</code>.
</div><div class="itemizedlist"><ul><li><div class="para">
<a class="xref" href="sect-Security_Guide-Firewalls.html" title="2.8. Firewalls">Section 2.8, “Firewalls”</a> — Contains a chapter about the role of firewalls within an overall security strategy as well as strategies for constructing firewall rules.
</div></li></ul></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Additional_Resources-Installed_IP_Tables_Documentation">2.9.7.1. Installed IP Tables Documentation</h4></div></div></div><a id="d0e16257" class="indexterm"/><div class="itemizedlist"><ul><li><div class="para">
<code class="command">man iptables</code> — Contains a description of <code class="command">iptables</code> as well as a comprehensive list of targets, options, and match extensions.
</div></li></ul></div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-IPTables-IPTables_and_IPv6.html"><strong>Prev</strong>2.9.6. IPTables and IPv6</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Additional_Resources-Useful_IP_Tables_Websites.html"><strong>Next</strong>2.9.7.2. Useful IP Tables Websites</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.9.3. Command Options for IPTables</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-IPTables.html" title="2.9. IPTables"/><link rel="prev" href="sect-Security_Guide-IPTables-Differences_Between_IPTables_and_IPChains.html" title="2.9.2. Differences Between IPTables and IPChains"/><link rel="next" href="sect-Security_Guide-Command_Options_for_IPTables-Command_Options.html" title="2.9.3.2. Command Options"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="
Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-IPTables-Differences_Between_IPTables_and_IPChains.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Command_Options_for_IPTables-Command_Options.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-IPTables-Command_Options_for_IPTables">2.9.3. Command Options for IPTables</h3></div></div></div><a id="d0e14355" class="indexterm"/><div class="para">
Rules for filtering packets are created using the <code class="command">iptables</code> command. The following aspects of the packet are most often used as criteria:
</div><div class="itemizedlist"><ul><li><div class="para">
<span class="emphasis"><em>Packet Type</em></span> — Specifies the type of packets the command filters.
</div></li><li><div class="para">
<span class="emphasis"><em>Packet Source/Destination</em></span> — Specifies which packets the command filters based on the source or destination of the packet.
</div></li><li><div class="para">
<span class="emphasis"><em>Target</em></span> — Specifies what action is taken on packets matching the above criteria.
</div></li></ul></div><div class="para">
Refer to <a class="xref" href="sect-Security_Guide-Command_Options_for_IPTables-IPTables_Match_Options.html" title="2.9.3.4. IPTables Match Options">Section 2.9.3.4, “IPTables Match Options”</a> and <a class="xref" href="sect-Security_Guide-Command_Options_for_IPTables-Target_Options.html" title="2.9.3.5. Target Options">Section 2.9.3.5, “Target Options”</a> for more information about specific options that address these aspects of a packet.
</div><div class="para">
The options used with specific <code class="command">iptables</code> rules must be grouped logically, based on the purpose and conditions of the overall rule, for the rule to be valid. The remainder of this section explains commonly-used options for the <code class="command">iptables</code> command.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Command_Options_for_IPTables-Structure_of_IPTables_Command_Options">2.9.3.1. Structure of IPTables Command Options</h4></div></div></div><a id="d0e14402" class="indexterm"/><div class="para">
Many <code class="command">iptables</code> commands have the following structure:
</div><pre class="screen"><code class="computeroutput"> iptables [-t <em class="replaceable"><code><table-name></code></em>] <em class="replaceable"><code><command></code></em> <em class="replaceable"><code><chain-name></code></em> \ <em class="replaceable"><code><parameter-1></code></em> <em class="replaceable"><code><option-1></code></em> \ <em class="replaceable"><code><parameter-n></code></em> <em class="replaceable"><code><option-n></code></em></code>
</pre><div class="para">
<em class="replaceable"><code><table-name></code></em> — Specifies which table the rule applies to. If omitted, the <code class="option">filter</code> table is used.
</div><div class="para">
<em class="replaceable"><code><command></code></em> — Specifies the action to perform, such as appending or deleting a rule.
</div><div class="para">
<em class="replaceable"><code><chain-name></code></em> — Specifies the chain to edit, create, or delete.
</div><div class="para">
<em class="replaceable"><code><parameter>-<option></code></em> pairs — Parameters and associated options that specify how to process a packet that matches the rule.
</div><div class="para">
The length and complexity of an <code class="command">iptables</code> command can change significantly, based on its purpose.
</div><div class="para">
For example, a command to remove a rule from a chain can be very short:
</div><div class="para">
<code class="command">iptables -D <em class="replaceable"><code><chain-name> <line-number></code></em></code>
</div><div class="para">
In contrast, a command that adds a rule which filters packets from a particular subnet using a variety of specific parameters and options can be rather long. When constructing <code class="command">iptables</code> commands, it is important to remember that some parameters and options require further parameters and options to construct a valid rule. This can produce a cascading effect, with the further parameters requiring yet more parameters. Until every parameter and option that requires another set of options is satisfied, the rule is not valid.
</div><div class="para">
Type <code class="command">iptables -h</code> to view a comprehensive list of <code class="command">iptables</code> command structures.
</div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-IPTables-Differences_Between_IPTables_and_IPChains.html"><strong>Prev</strong>2.9.2. Differences Between IPTables and IPChains</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Command_Options_for_IPTables-Command_Options.html"><strong>Next</strong>2.9.3.2. Command Options</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.9.2. Differences Between IPTables and IPChains</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-IPTables.html" title="2.9. IPTables"/><link rel="prev" href="sect-Security_Guide-IPTables.html" title="2.9. IPTables"/><link rel="next" href="sect-Security_Guide-IPTables-Command_Options_for_IPTables.html" title="2.9.3. Command Options for IPTables"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="p
revious"><a accesskey="p" href="sect-Security_Guide-IPTables.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables-Command_Options_for_IPTables.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-IPTables-Differences_Between_IPTables_and_IPChains">2.9.2. Differences Between IPTables and IPChains</h3></div></div></div><a id="d0e14256" class="indexterm"/><div class="para">
Both <code class="command">ipchains</code> and <code class="command">iptables</code> use chains of rules that operate within the Linux kernel to filter packets based on matches with specified rules or rule sets. However, <code class="command">iptables</code> offers a more extensible way of filtering packets, giving the administrator greater control without building undue complexity into the system.
</div><div class="para">
You should be aware of the following significant differences between <code class="command">ipchains</code> and <code class="command">iptables</code>:
</div><div class="variablelist"><dl><dt><span class="term"><span class="emphasis"><em>Using <code class="command">iptables</code>, each filtered packet is processed using rules from only one chain rather than multiple chains.</em></span></span></dt><dd><div class="para">
For example, a FORWARD packet coming into a system using <code class="command">ipchains</code> would have to go through the INPUT, FORWARD, and OUTPUT chains to continue to its destination. However, <code class="command">iptables</code> only sends packets to the INPUT chain if they are destined for the local system, and only sends them to the OUTPUT chain if the local system generated the packets. It is therefore important to place the rule designed to catch a particular packet within the chain that actually handles the packet.
</div></dd><dt><span class="term"><span class="emphasis"><em>The DENY target has been changed to DROP.</em></span></span></dt><dd><div class="para">
In <code class="command">ipchains</code>, packets that matched a rule in a chain could be directed to the DENY target. This target must be changed to DROP in <code class="command">iptables</code>.
</div></dd><dt><span class="term"><span class="emphasis"><em>Order matters when placing options in a rule.</em></span></span></dt><dd><div class="para">
In <code class="command">ipchains</code>, the order of the rule options does not matter.
</div><div class="para">
The <code class="command">iptables</code> command has a stricter syntax. The <code class="command">iptables</code> command requires that the protocol (ICMP, TCP, or UDP) be specified before the source or destination ports.
</div></dd><dt><span class="term"><span class="emphasis"><em>Network interfaces must be associated with the correct chains in firewall rules.</em></span></span></dt><dd><div class="para">
For example, incoming interfaces (<code class="option">-i</code> option) can only be used in INPUT or FORWARD chains. Similarly, outgoing interfaces (<code class="option">-o</code> option) can only be used in FORWARD or OUTPUT chains.
</div><div class="para">
In other words, INPUT chains and incoming interfaces work together; OUTPUT chains and outgoing interfaces work together. FORWARD chains work with both incoming and outgoing interfaces.
</div><div class="para">
OUTPUT chains are no longer used by incoming interfaces, and INPUT chains are not seen by packets moving through outgoing interfaces.
</div></dd></dl></div><div class="para">
This is not a comprehensive list of the changes. Refer to <a class="xref" href="sect-Security_Guide-IPTables-Additional_Resources.html" title="2.9.7. Additional Resources">Section 2.9.7, “Additional Resources”</a> for more specific information.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-IPTables.html"><strong>Prev</strong>2.9. IPTables</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables-Command_Options_for_IPTables.html"><strong>Next</strong>2.9.3. Command Options for IPTables</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.9.5. IPTables Control Scripts</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-IPTables.html" title="2.9. IPTables"/><link rel="prev" href="sect-Security_Guide-IPTables-Saving_IPTables_Rules.html" title="2.9.4. Saving IPTables Rules"/><link rel="next" href="sect-Security_Guide-IPTables-IPTables_and_IPv6.html" title="2.9.6. IPTables and IPv6"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="pre
vious"><a accesskey="p" href="sect-Security_Guide-IPTables-Saving_IPTables_Rules.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables-IPTables_and_IPv6.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-IPTables-IPTables_Control_Scripts">2.9.5. IPTables Control Scripts</h3></div></div></div><a id="d0e15749" class="indexterm"/><a id="d0e15757" class="indexterm"/><a id="d0e15765" class="indexterm"/><a id="d0e15773" class="indexterm"/><a id="d0e15781" class="indexterm"/><a id="d0e15789" class="indexterm"/><a id="d0e15797" class="indexterm"/><a id="d0e15805" class="indexterm"/><a id="d0e15813" class="indexterm"/><a id="d0e15821" class="indexterm"/><a id="d0e15829" class="indexterm"/><a id="d0e15837" class="indexterm"/><div class="para">
There are two basic methods for controlling <code class="command">iptables</code> in Fedora:
</div><div class="itemizedlist"><ul><li><div class="para">
<span class="application"><strong>Security Level Configuration Tool</strong></span> (<code class="command">system-config-securitylevel</code>) — A graphical interface for creating, activating, and saving basic firewall rules. Refer to <a class="xref" href="sect-Security_Guide-Firewalls-Basic_Firewall_Configuration.html" title="2.8.2. Basic Firewall Configuration">Section 2.8.2, “Basic Firewall Configuration”</a> for more information.
</div></li><li><div class="para">
<code class="command">/sbin/service iptables <em class="replaceable"><code><option></code></em></code> — Used to manipulate various functions of <code class="command">iptables</code> using its initscript. The following options are available:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="command">start</code> — If a firewall is configured (that is, <code class="filename">/etc/sysconfig/iptables</code> exists), all running <code class="command">iptables</code> are stopped completely and then started using the <code class="command">/sbin/iptables-restore</code> command. This option only works if the <code class="command">ipchains</code> kernel module is not loaded. To check if this module is loaded, type the following command as root:
</div><pre class="screen"><code class="command"> [root@MyServer ~]# lsmod | grep ipchains </code>
</pre><div class="para">
If this command returns no output, it means the module is not loaded. If necessary, use the <code class="command">/sbin/rmmod</code> command to remove the module.
</div></li><li><div class="para">
<code class="command">stop</code> — If a firewall is running, the firewall rules in memory are flushed, and all iptables modules and helpers are unloaded.
</div><div class="para">
If the <code class="command">IPTABLES_SAVE_ON_STOP</code> directive in the <code class="filename">/etc/sysconfig/iptables-config</code> configuration file is changed from its default value to <code class="command">yes</code>, current rules are saved to <code class="filename">/etc/sysconfig/iptables</code> and any existing rules are moved to the file <code class="filename">/etc/sysconfig/iptables.save</code>.
</div><div class="para">
Refer to <a class="xref" href="sect-Security_Guide-IPTables-IPTables_Control_Scripts.html#sect-Security_Guide-IPTables_Control_Scripts-IPTables_Control_Scripts_Configuration_File" title="2.9.5.1. IPTables Control Scripts Configuration File">Section 2.9.5.1, “IPTables Control Scripts Configuration File”</a> for more information about the <code class="filename">iptables-config</code> file.
</div></li><li><div class="para">
<code class="command">restart</code> — If a firewall is running, the firewall rules in memory are flushed, and the firewall is started again if it is configured in <code class="filename">/etc/sysconfig/iptables</code>. This option only works if the <code class="command">ipchains</code> kernel module is not loaded.
</div><div class="para">
If the <code class="command">IPTABLES_SAVE_ON_RESTART</code> directive in the <code class="filename">/etc/sysconfig/iptables-config</code> configuration file is changed from its default value to <code class="command">yes</code>, current rules are saved to <code class="filename">/etc/sysconfig/iptables</code> and any existing rules are moved to the file <code class="filename">/etc/sysconfig/iptables.save</code>.
</div><div class="para">
Refer to <a class="xref" href="sect-Security_Guide-IPTables-IPTables_Control_Scripts.html#sect-Security_Guide-IPTables_Control_Scripts-IPTables_Control_Scripts_Configuration_File" title="2.9.5.1. IPTables Control Scripts Configuration File">Section 2.9.5.1, “IPTables Control Scripts Configuration File”</a> for more information about the <code class="filename">iptables-config</code> file.
</div></li><li><div class="para">
<code class="command">status</code> — Displays the status of the firewall and lists all active rules.
</div><div class="para">
The default configuration for this option displays IP addresses in each rule. To display domain and hostname information, edit the <code class="filename">/etc/sysconfig/iptables-config</code> file and change the value of <code class="command">IPTABLES_STATUS_NUMERIC</code> to <code class="command">no</code>. Refer to <a class="xref" href="sect-Security_Guide-IPTables-IPTables_Control_Scripts.html#sect-Security_Guide-IPTables_Control_Scripts-IPTables_Control_Scripts_Configuration_File" title="2.9.5.1. IPTables Control Scripts Configuration File">Section 2.9.5.1, “IPTables Control Scripts Configuration File”</a> for more information about the <code class="filename">iptables-config</code> file.
</div></li><li><div class="para">
<code class="command">panic</code> — Flushes all firewall rules. The policy of all configured tables is set to <code class="command">DROP</code>.
</div><div class="para">
This option could be useful if a server is known to be compromised. Rather than physically disconnecting from the network or shutting down the system, you can use this option to stop all further network traffic but leave the machine in a state ready for analysis or other forensics.
</div></li><li><div class="para">
<code class="command">save</code> — Saves firewall rules to <code class="filename">/etc/sysconfig/iptables</code> using <code class="command">iptables-save</code>. Refer to <a class="xref" href="sect-Security_Guide-IPTables-Saving_IPTables_Rules.html" title="2.9.4. Saving IPTables Rules">Section 2.9.4, “Saving IPTables Rules”</a> for more information.
</div></li></ul></div></li></ul></div><div class="tip"><h2>Tip</h2><div class="para">
To use the same initscript commands to control netfilter for IPv6, substitute <code class="command">ip6tables</code> for <code class="command">iptables</code> in the <code class="command">/sbin/service</code> commands listed in this section. For more information about IPv6 and netfilter, refer to <a class="xref" href="sect-Security_Guide-IPTables-IPTables_and_IPv6.html" title="2.9.6. IPTables and IPv6">Section 2.9.6, “IPTables and IPv6”</a>.
</div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-IPTables_Control_Scripts-IPTables_Control_Scripts_Configuration_File">2.9.5.1. IPTables Control Scripts Configuration File</h4></div></div></div><a id="d0e16033" class="indexterm"/><div class="para">
The behavior of the <code class="command">iptables</code> initscripts is controlled by the <code class="filename">/etc/sysconfig/iptables-config</code> configuration file. The following is a list of directives contained in this file:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="command">IPTABLES_MODULES</code> — Specifies a space-separated list of additional <code class="command">iptables</code> modules to load when a firewall is activated. These can include connection tracking and NAT helpers.
</div></li><li><div class="para">
<code class="command">IPTABLES_MODULES_UNLOAD</code> — Unloads modules on restart and stop. This directive accepts the following values:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="command">yes</code> — The default value. This option must be set to achieve a correct state for a firewall restart or stop.
</div></li><li><div class="para">
<code class="command">no</code> — This option should only be set if there are problems unloading the netfilter modules.
</div></li></ul></div></li><li><div class="para">
<code class="command">IPTABLES_SAVE_ON_STOP</code> — Saves current firewall rules to <code class="filename">/etc/sysconfig/iptables</code> when the firewall is stopped. This directive accepts the following values:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="command">yes</code> — Saves existing rules to <code class="filename">/etc/sysconfig/iptables</code> when the firewall is stopped, moving the previous version to the <code class="filename">/etc/sysconfig/iptables.save</code> file.
</div></li><li><div class="para">
<code class="command">no</code> — The default value. Does not save existing rules when the firewall is stopped.
</div></li></ul></div></li><li><div class="para">
<code class="command">IPTABLES_SAVE_ON_RESTART</code> — Saves current firewall rules when the firewall is restarted. This directive accepts the following values:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="command">yes</code> — Saves existing rules to <code class="filename">/etc/sysconfig/iptables</code> when the firewall is restarted, moving the previous version to the <code class="filename">/etc/sysconfig/iptables.save</code> file.
</div></li><li><div class="para">
<code class="command">no</code> — The default value. Does not save existing rules when the firewall is restarted.
</div></li></ul></div></li><li><div class="para">
<code class="command">IPTABLES_SAVE_COUNTER</code> — Saves and restores all packet and byte counters in all chains and rules. This directive accepts the following values:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="command">yes</code> — Saves the counter values.
</div></li><li><div class="para">
<code class="command">no</code> — The default value. Does not save the counter values.
</div></li></ul></div></li><li><div class="para">
<code class="command">IPTABLES_STATUS_NUMERIC</code> — Outputs IP addresses in numeric form instead of domain or hostnames. This directive accepts the following values:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="command">yes</code> — The default value. Returns only IP addresses within a status output.
</div></li><li><div class="para">
<code class="command">no</code> — Returns domain or hostnames within a status output.
</div></li></ul></div></li></ul></div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-IPTables-Saving_IPTables_Rules.html"><strong>Prev</strong>2.9.4. Saving IPTables Rules</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables-IPTables_and_IPv6.html"><strong>Next</strong>2.9.6. IPTables and IPv6</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.9.6. IPTables and IPv6</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-IPTables.html" title="2.9. IPTables"/><link rel="prev" href="sect-Security_Guide-IPTables-IPTables_Control_Scripts.html" title="2.9.5. IPTables Control Scripts"/><link rel="next" href="sect-Security_Guide-IPTables-Additional_Resources.html" title="2.9.7. Additional Resources"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class
="previous"><a accesskey="p" href="sect-Security_Guide-IPTables-IPTables_Control_Scripts.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables-Additional_Resources.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-IPTables-IPTables_and_IPv6">2.9.6. IPTables and IPv6</h3></div></div></div><a id="d0e16173" class="indexterm"/><div class="para">
If the <code class="filename">iptables-ipv6</code> package is installed, netfilter in Fedora can filter the next-generation IPv6 Internet protocol. The command used to manipulate the IPv6 netfilter is <code class="command">ip6tables</code>.
</div><div class="para">
Most directives for this command are identical to those used for <code class="command">iptables</code>, except the <code class="command">nat</code> table is not yet supported. This means that it is not yet possible to perform IPv6 network address translation tasks, such as masquerading and port forwarding.
</div><div class="para">
Rules for <code class="command">ip6tables</code> are saved in the <code class="filename">/etc/sysconfig/ip6tables</code> file. Previous rules saved by the <code class="command">ip6tables</code> initscripts are saved in the <code class="filename">/etc/sysconfig/ip6tables.save</code> file.
</div><div class="para">
Configuration options for the <code class="command">ip6tables</code> init script are stored in <code class="filename">/etc/sysconfig/ip6tables-config</code>, and the names for each directive vary slightly from their <code class="command">iptables</code> counterparts.
</div><div class="para">
For example, the <code class="filename">iptables-config</code> directive <code class="command">IPTABLES_MODULES</code>:the equivalent in the <code class="filename">ip6tables-config</code> file is <code class="command">IP6TABLES_MODULES</code>.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-IPTables-IPTables_Control_Scripts.html"><strong>Prev</strong>2.9.5. IPTables Control Scripts</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables-Additional_Resources.html"><strong>Next</strong>2.9.7. Additional Resources</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.9.4. Saving IPTables Rules</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-IPTables.html" title="2.9. IPTables"/><link rel="prev" href="sect-Security_Guide-Command_Options_for_IPTables-Listing_Options.html" title="2.9.3.6. Listing Options"/><link rel="next" href="sect-Security_Guide-IPTables-IPTables_Control_Scripts.html" title="2.9.5. IPTables Control Scripts"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="d
ocnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Command_Options_for_IPTables-Listing_Options.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables-IPTables_Control_Scripts.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-IPTables-Saving_IPTables_Rules">2.9.4. Saving IPTables Rules</h3></div></div></div><a id="d0e15584" class="indexterm"/><a id="d0e15590" class="indexterm"/><a id="d0e15598" class="indexterm"/><a id="d0e15605" class="indexterm"/><a id="d0e15612" class="indexterm"/><a id="d0e15620" class="indexterm"/><a id="d0e15629" class="indexterm"/><div class="para">
Rules created with the <code class="command">iptables</code> command are stored in memory. If the system is restarted before saving the <code class="command">iptables</code> rule set, all rules are lost. For netfilter rules to persist through a system reboot, they need to be saved. To save netfilter rules, type the following command as root:
</div><pre class="screen"><code class="command"> /sbin/service iptables save </code>
</pre><div class="para">
This executes the <code class="command">iptables</code> init script, which runs the <code class="command">/sbin/iptables-save</code> program and writes the current <code class="command">iptables</code> configuration to <code class="filename">/etc/sysconfig/iptables</code>. The existing <code class="filename">/etc/sysconfig/iptables</code> file is saved as <code class="filename">/etc/sysconfig/iptables.save</code>.
</div><div class="para">
The next time the system boots, the <code class="command">iptables</code> init script reapplies the rules saved in <code class="filename">/etc/sysconfig/iptables</code> by using the <code class="command">/sbin/iptables-restore</code> command.
</div><div class="para">
While it is always a good idea to test a new <code class="command">iptables</code> rule before committing it to the <code class="filename">/etc/sysconfig/iptables</code> file, it is possible to copy <code class="command">iptables</code> rules into this file from another system's version of this file. This provides a quick way to distribute sets of <code class="command">iptables</code> rules to multiple machines.
</div><div class="para">
You can also save the iptables rules to a separate file for distribution, backup or other purposes. To save your iptables rules, type the following command as root:
</div><pre class="screen"><code class="command"> [root@myserver ~]# iptables-save > <em class="replaceable"><code><filename></code></em></code>where <em class="replaceable"><code><filename></code></em> is a user-defined name for your ruleset.
</pre><div class="important"><h2>Important</h2><div class="para">
If distributing the <code class="filename">/etc/sysconfig/iptables</code> file to other machines, type <code class="command">/sbin/service iptables restart</code> for the new rules to take effect.
</div></div><div class="note"><h2>Note</h2><div class="para">
Note the difference between the <code class="command">iptables</code> <span class="emphasis"><em>command</em></span> (<code class="command">/sbin/iptables</code>), which is used to manipulate the tables and chains that constitute the <code class="command">iptables</code> functionality, and the <code class="command">iptables</code> <span class="emphasis"><em>service</em></span> (<code class="command">/sbin/iptables service</code>), which is used to enable and disable the <code class="command">iptables</code> service itself.
</div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Command_Options_for_IPTables-Listing_Options.html"><strong>Prev</strong>2.9.3.6. Listing Options</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables-IPTables_Control_Scripts.html"><strong>Next</strong>2.9.5. IPTables Control Scripts</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.9. IPTables</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="chap-Security_Guide-Securing_Your_Network.html" title="Chapter 2. Securing Your Network"/><link rel="prev" href="sect-Security_Guide-Additional_Resources-Related_Documentation.html" title="2.8.9.3. Related Documentation"/><link rel="next" href="sect-Security_Guide-IPTables-Differences_Between_IPTables_and_IPChains.html" title="2.9.2. Differences Between IPTables and IPChains"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_r
ight.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Additional_Resources-Related_Documentation.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables-Differences_Between_IPTables_and_IPChains.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-IPTables">2.9. IPTables</h2></div></div></div><a id="d0e13957" class="indexterm"/><a id="d0e13963" class="indexterm"/><a id="d0e13969" class="indexterm"/><div class="para">
Included with Fedora are advanced tools for network <em class="firstterm">packet filtering</em> — the process of controlling network packets as they enter, move through, and exit the network stack within the kernel. Kernel versions prior to 2.4 relied on <code class="command">ipchains</code> for packet filtering and used lists of rules applied to packets at each step of the filtering process. The 2.4 kernel introduced <code class="command">iptables</code> (also called <em class="firstterm">netfilter</em>), which is similar to <code class="command">ipchains</code> but greatly expands the scope and control available for filtering network packets.
</div><div class="para">
This chapter focuses on packet filtering basics, defines the differences between <code class="command">ipchains</code> and <code class="command">iptables</code>, explains various options available with <code class="command">iptables</code> commands, and explains how filtering rules can be preserved between system reboots.
</div><div class="para">
Refer to <a class="xref" href="sect-Security_Guide-IPTables-Additional_Resources.html" title="2.9.7. Additional Resources">Section 2.9.7, “Additional Resources”</a> for instructions on how to construct <code class="command">iptables</code> rules and setting up a firewall based on these rules.
</div><div class="warning"><h2>Warning</h2><div class="para">
The default firewall mechanism in the 2.4 and later kernels is <code class="command">iptables</code>, but <code class="command">iptables</code> cannot be used if <code class="command">ipchains</code> is already running. If <code class="command">ipchains</code> is present at boot time, the kernel issues an error and fails to start <code class="command">iptables</code>.
</div><div class="para">
The functionality of <code class="command">ipchains</code> is not affected by these errors.
</div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-IPTables-Packet_Filtering">2.9.1. Packet Filtering</h3></div></div></div><a id="d0e14039" class="indexterm"/><a id="d0e14045" class="indexterm"/><a id="d0e14051" class="indexterm"/><a id="d0e14057" class="indexterm"/><a id="d0e14063" class="indexterm"/><div class="para">
The Linux kernel uses the <span class="application"><strong>Netfilter</strong></span> facility to filter packets, allowing some of them to be received by or pass through the system while stopping others. This facility is built in to the Linux kernel, and has three built-in <em class="firstterm">tables</em> or <em class="firstterm">rules lists</em>, as follows:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">filter</code> — The default table for handling network packets.
</div></li><li><div class="para">
<code class="option">nat</code> — Used to alter packets that create a new connection and used for <em class="firstterm">Network Address Translation</em> (<em class="firstterm">NAT</em>).
</div></li><li><div class="para">
<code class="option">mangle</code> — Used for specific types of packet alteration.
</div></li></ul></div><div class="para">
Each table has a group of built-in <em class="firstterm">chains</em>, which correspond to the actions performed on the packet by <code class="command">netfilter</code>.
</div><div class="para">
The built-in chains for the <code class="option">filter</code> table are as follows:
</div><div class="itemizedlist"><ul><li><div class="para">
<em class="firstterm">INPUT</em> — Applies to network packets that are targeted for the host.
</div></li><li><div class="para">
<em class="firstterm">OUTPUT</em> — Applies to locally-generated network packets.
</div></li><li><div class="para">
<em class="firstterm">FORWARD</em> — Applies to network packets routed through the host.
</div></li></ul></div><div class="para">
The built-in chains for the <code class="option">nat</code> table are as follows:
</div><div class="itemizedlist"><ul><li><div class="para">
<em class="firstterm">PREROUTING</em> — Alters network packets when they arrive.
</div></li><li><div class="para">
<em class="firstterm">OUTPUT</em> — Alters locally-generated network packets before they are sent out.
</div></li><li><div class="para">
<em class="firstterm">POSTROUTING</em> — Alters network packets before they are sent out.
</div></li></ul></div><div class="para">
The built-in chains for the <code class="option">mangle</code> table are as follows:
</div><div class="itemizedlist"><ul><li><div class="para">
<em class="firstterm">INPUT</em> — Alters network packets targeted for the host.
</div></li><li><div class="para">
<em class="firstterm">OUTPUT</em> — Alters locally-generated network packets before they are sent out.
</div></li><li><div class="para">
<em class="firstterm">FORWARD</em> — Alters network packets routed through the host.
</div></li><li><div class="para">
<em class="firstterm">PREROUTING</em> — Alters incoming network packets before they are routed.
</div></li><li><div class="para">
<em class="firstterm">POSTROUTING</em> — Alters network packets before they are sent out.
</div></li></ul></div><div class="para">
Every network packet received by or sent from a Linux system is subject to at least one table. However, a packet may be subjected to multiple rules within each table before emerging at the end of the chain. The structure and purpose of these rules may vary, but they usually seek to identify a packet coming from or going to a particular IP address, or set of addresses, when using a particular protocol and network service.
</div><div class="note"><h2>Note</h2><div class="para">
By default, firewall rules are saved in the <code class="filename">/etc/sysconfig/iptables</code> or <code class="filename">/etc/sysconfig/ip6tables</code> files.
</div><div class="para">
The <code class="command">iptables</code> service starts before any DNS-related services when a Linux system is booted. This means that firewall rules can only reference numeric IP addresses (for example, 192.168.0.1). Domain names (for example, host.example.com) in such rules produce errors.
</div></div><div class="para">
Regardless of their destination, when packets match a particular rule in one of the tables, a <em class="firstterm">target</em> or action is applied to them. If the rule specifies an <code class="command">ACCEPT</code> target for a matching packet, the packet skips the rest of the rule checks and is allowed to continue to its destination. If a rule specifies a <code class="command">DROP</code> target, that packet is refused access to the system and nothing is sent back to the host that sent the packet. If a rule specifies a <code class="command">QUEUE</code> target, the packet is passed to user-space. If a rule specifies the optional <code class="command">REJECT</code> target, the packet is dropped, but an error packet is sent to the packet's originator.
</div><div class="para">
Every chain has a default policy to <code class="command">ACCEPT</code>, <code class="command">DROP</code>, <code class="command">REJECT</code>, or <code class="command">QUEUE</code>. If none of the rules in the chain apply to the packet, then the packet is dealt with in accordance with the default policy.
</div><div class="para">
The <code class="command">iptables</code> command configures these tables, as well as sets up new tables if necessary.
</div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Additional_Resources-Related_Documentation.html"><strong>Prev</strong>2.8.9.3. Related Documentation</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables-Differences_Between_IPTables_and_IPChains.html"><strong>Next</strong>2.9.2. Differences Between IPTables and IPChains</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.9.3.4.4. Additional Match Option Modules</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Command_Options_for_IPTables-IPTables_Match_Options.html" title="2.9.3.4. IPTables Match Options"/><link rel="prev" href="sect-Security_Guide-IPTables_Match_Options-ICMP_Protocol.html" title="2.9.3.4.3. ICMP Protocol"/><link rel="next" href="sect-Security_Guide-Command_Options_for_IPTables-Target_Options.html" title="2.9.3.5. Target Options"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/i
mages/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-IPTables_Match_Options-ICMP_Protocol.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Command_Options_for_IPTables-Target_Options.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-IPTables_Match_Options-Additional_Match_Option_Modules">2.9.3.4.4. Additional Match Option Modules</h5></div></div></div><a id="d0e15192" class="indexterm"/><div class="para">
Additional match options are available through modules loaded by the <code class="command">iptables</code> command.
</div><div class="para">
To use a match option module, load the module by name using the <code class="option">-m <em class="replaceable"><code><module-name></code></em></code>, where <em class="replaceable"><code><module-name></code></em> is the name of the module.
</div><div class="para">
Many modules are available by default. You can also create modules to provide additional functionality.
</div><div class="para">
The following is a partial list of the most commonly used modules:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">limit</code> module — Places limits on how many packets are matched to a particular rule.
</div><div class="para">
When used in conjunction with the <code class="command">LOG</code> target, the <code class="option">limit</code> module can prevent a flood of matching packets from filling up the system log with repetitive messages or using up system resources.
</div><div class="para">
Refer to <a class="xref" href="sect-Security_Guide-Command_Options_for_IPTables-Target_Options.html" title="2.9.3.5. Target Options">Section 2.9.3.5, “Target Options”</a> for more information about the <code class="command">LOG</code> target.
</div><div class="para">
The <code class="option">limit</code> module enables the following options:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">--limit</code> — Sets the maximum number of matches for a particular time period, specified as a <code class="option"><em class="replaceable"><code><value>/<period></code></em></code> pair. For example, using <code class="option">--limit 5/hour</code> allows five rule matches per hour.
</div><div class="para">
Periods can be specified in seconds, minutes, hours, or days.
</div><div class="para">
If a number and time modifier are not used, the default value of <code class="option">3/hour</code> is assumed.
</div></li><li><div class="para">
<code class="option">--limit-burst</code> — Sets a limit on the number of packets able to match a rule at one time.
</div><div class="para">
This option is specified as an integer and should be used in conjunction with the <code class="option">--limit</code> option.
</div><div class="para">
If no value is specified, the default value of five (5) is assumed.
</div></li></ul></div></li><li><div class="para">
<code class="option">state</code> module — Enables state matching.
</div><div class="para">
The <code class="option">state</code> module enables the following options:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">--state</code> — match a packet with the following connection states:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">ESTABLISHED</code> — The matching packet is associated with other packets in an established connection. You need to accept this state if you want to maintain a connection between a client and a server.
</div></li><li><div class="para">
<code class="option">INVALID</code> — The matching packet cannot be tied to a known connection.
</div></li><li><div class="para">
<code class="option">NEW</code> — The matching packet is either creating a new connection or is part of a two-way connection not previously seen. You need to accept this state if you want to allow new connections to a service.
</div></li><li><div class="para">
<code class="option">RELATED</code> — The matching packet is starting a new connection related in some way to an existing connection. An example of this is FTP, which uses one connection for control traffic (port 21), and a separate connection for data transfer (port 20).
</div></li></ul></div><div class="para">
These connection states can be used in combination with one another by separating them with commas, such as <code class="option">-m state --state INVALID,NEW</code>.
</div></li></ul></div></li><li><div class="para">
<code class="option">mac</code> module — Enables hardware MAC address matching.
</div><div class="para">
The <code class="option">mac</code> module enables the following option:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">--mac-source</code> — Matches a MAC address of the network interface card that sent the packet. To exclude a MAC address from a rule, place an exclamation point character (<code class="option">!</code>) after the <code class="option">--mac-source</code> match option.
</div></li></ul></div></li></ul></div><div class="para">
Refer to the <code class="command">iptables</code> man page for more match options available through modules.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-IPTables_Match_Options-ICMP_Protocol.html"><strong>Prev</strong>2.9.3.4.3. ICMP Protocol</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Command_Options_for_IPTables-Target_Options.html"><strong>Next</strong>2.9.3.5. Target Options</a></li></ul></body></html>
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_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-IPTables_Match_Options-UDP_Protocol.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables_Match_Options-Additional_Match_Option_Modules.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-IPTables_Match_Options-ICMP_Protocol">2.9.3.4.3. ICMP Protocol</h5></div></div></div><a id="d0e15166" class="indexterm"/><div class="para">
The following match options are available for the Internet Control Message Protocol (ICMP) (<code class="option">-p icmp</code>):
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">--icmp-type</code> — Sets the name or number of the ICMP type to match with the rule. A list of valid ICMP names can be retrieved by typing the <code class="command">iptables -p icmp -h</code> command.
</div></li></ul></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-IPTables_Match_Options-UDP_Protocol.html"><strong>Prev</strong>2.9.3.4.2. UDP Protocol</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables_Match_Options-Additional_Match_Option_Modules.html"><strong>Next</strong>2.9.3.4.4. Additional Match Option Modules</a></li></ul></body></html>
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es/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Command_Options_for_IPTables-IPTables_Match_Options.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables_Match_Options-ICMP_Protocol.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-IPTables_Match_Options-UDP_Protocol">2.9.3.4.2. UDP Protocol</h5></div></div></div><a id="d0e15114" class="indexterm"/><div class="para">
These match options are available for the UDP protocol (<code class="option">-p udp</code>):
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">--dport</code> — Specifies the destination port of the UDP packet, using the service name, port number, or range of port numbers. The <code class="option">--destination-port</code> match option is synonymous with <code class="option">--dport</code>.
</div></li><li><div class="para">
<code class="option">--sport</code> — Specifies the source port of the UDP packet, using the service name, port number, or range of port numbers. The <code class="option">--source-port</code> match option is synonymous with <code class="option">--sport</code>.
</div></li></ul></div><div class="para">
For the <code class="option">--dport</code> and <code class="option">--sport</code> options, to specify a range of port numbers, separate the two numbers with a colon (:). For example: <code class="option">-p tcp --dport 3000:3200</code>. The largest acceptable valid range is 0:65535.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Command_Options_for_IPTables-IPTables_Match_Options.html"><strong>Prev</strong>2.9.3.4. IPTables Match Options</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-IPTables_Match_Options-ICMP_Protocol.html"><strong>Next</strong>2.9.3.4.3. ICMP Protocol</a></li></ul></body></html>
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The first step in creating a connection is to gather system and network information from each workstation. For a host-to-host connection, you need the following:
</div><div class="itemizedlist"><ul><li><div class="para">
The IP address of each host
</div></li><li><div class="para">
A unique name, for example, <code class="computeroutput">ipsec1</code>. This is used to identify the <abbr class="abbrev">IPsec</abbr> connection and to distinguish it from other devices or connections.
</div></li><li><div class="para">
A fixed encryption key or one automatically generated by <code class="command">racoon</code>.
</div></li><li><div class="para">
A pre-shared authentication key that is used during the initial stage of the connection and to exchange encryption keys during the session.
</div></li></ul></div><div class="para">
For example, suppose Workstation A and Workstation B want to connect to each other through an <abbr class="abbrev">IPsec</abbr> tunnel. They want to connect using a pre-shared key with the value of <code class="computeroutput">Key_Value01</code>, and the users agree to let <code class="command">racoon</code> automatically generate and share an authentication key between each host. Both host users decide to name their connections <code class="computeroutput">ipsec1</code>.
</div><div class="note"><h2>Note</h2><div class="para">
You should choose a PSK that uses a mixture of upper- and lower-case characters, numbers and punctuation. An easily-guessable PSK constitutes a security risk.
</div><div class="para">
It is not necessary to use the same connection name for each host. You should choose a name that is convenient and meaningful for your installation.
</div></div><div class="para">
The following is the <abbr class="abbrev">IPsec</abbr> configuration file for Workstation A for a host-to-host <abbr class="abbrev">IPsec</abbr> connection with Workstation B. The unique name to identify the connection in this example is <em class="replaceable"><code>ipsec1</code></em>, so the resulting file is called <code class="filename">/etc/sysconfig/network-scripts/ifcfg-ipsec1</code>.
</div><pre class="screen">DST=<em class="replaceable"><code>X.X.X.X</code></em>TYPE=IPSEC
ONBOOT=no
IKE_METHOD=PSK
</pre><div class="para">
For Workstation A, <em class="replaceable"><code>X.X.X.X</code></em> is the IP address of Workstation B. For Workstation B, <em class="replaceable"><code>X.X.X.X</code></em> is the IP address of Workstation A. This connection is not set to initiate on boot-up (<code class="computeroutput">ONBOOT=no</code>) and it uses the pre-shared key method of authentication (<code class="computeroutput">IKE_METHOD=PSK</code>).
</div><div class="para">
The following is the content of the pre-shared key file (called <code class="filename">/etc/sysconfig/network-scripts/keys-ipsec1</code>) that both workstations need to authenticate each other. The contents of this file should be identical on both workstations, and only the root user should be able to read or write this file.
</div><pre class="screen">IKE_PSK=Key_Value01
</pre><div class="important"><h2>Important</h2><div class="para">
To change the <code class="filename">keys-ipsec1</code> file so that only the root user can read or edit the file, use the following command after creating the file:
</div><pre class="screen">[root@myServer ~] # chmod 600 /etc/sysconfig/network-scripts/keys-ipsec1
</pre></div><div class="para">
To change the authentication key at any time, edit the <code class="filename">keys-ipsec1</code> file on both workstations. <span class="emphasis"><em>Both authentication keys must be identical for proper connectivity</em></span>.
</div><div class="para">
The next example shows the specific configuration for the phase 1 connection to the remote host. The file is called <code class="filename"><em class="replaceable"><code>X.X.X.X</code></em>.conf</code>, where <em class="replaceable"><code>X.X.X.X</code></em> is the IP address of the remote <abbr class="abbrev">IPsec</abbr> host. Note that this file is automatically generated when the <abbr class="abbrev">IPsec</abbr> tunnel is activated and should not be edited directly.
</div><pre class="screen">remote <em class="replaceable"><code>X.X.X.X</code></em>{
exchange_mode aggressive, main;
my_identifier address;
proposal {
encryption_algorithm 3des;
hash_algorithm sha1;
authentication_method pre_shared_key;
dh_group 2 ;
}
}
</pre><div class="para">
The default phase 1 configuration file that is created when an <abbr class="abbrev">IPsec</abbr> connection is initialized contains the following statements used by the Fedora implementation of IPsec:
</div><div class="variablelist"><dl><dt><span class="term">remote <em class="replaceable"><code>X.X.X.X</code></em></span></dt><dd><div class="para">
Specifies that the subsequent stanzas of this configuration file apply only to the remote node identified by the <em class="replaceable"><code>X.X.X.X</code></em> IP address.
</div></dd><dt><span class="term">exchange_mode aggressive</span></dt><dd><div class="para">
The default configuration for <abbr class="abbrev">IPsec</abbr> on Fedora uses an aggressive authentication mode, which lowers the connection overhead while allowing configuration of several <abbr class="abbrev">IPsec</abbr> connections with multiple hosts.
</div></dd><dt><span class="term">my_identifier address</span></dt><dd><div class="para">
Specifies the identification method to use when authenticating nodes. Fedora uses IP addresses to identify nodes.
</div></dd><dt><span class="term">encryption_algorithm 3des</span></dt><dd><div class="para">
Specifies the encryption cipher used during authentication. By default, <em class="firstterm">Triple Data Encryption Standard</em> (<acronym class="acronym">3DES</acronym>) is used.
</div></dd><dt><span class="term">hash_algorithm sha1;</span></dt><dd><div class="para">
Specifies the hash algorithm used during phase 1 negotiation between nodes. By default, Secure Hash Algorithm version 1 is used.
</div></dd><dt><span class="term">authentication_method pre_shared_key</span></dt><dd><div class="para">
Specifies the authentication method used during node negotiation. By default, Fedora uses pre-shared keys for authentication.
</div></dd><dt><span class="term">dh_group 2</span></dt><dd><div class="para">
Specifies the Diffie-Hellman group number for establishing dynamically-generated session keys. By default, modp1024 (group 2) is used.
</div></dd></dl></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Manual_IPsec_Host_to_Host_Configuration-The_Racoon_Configuration_File">2.7.6.2.1. The Racoon Configuration File</h5></div></div></div><div class="para">
The <code class="filename">/etc/racoon/racoon.conf</code> files should be identical on all <abbr class="abbrev">IPsec</abbr> nodes <span class="emphasis"><em>except</em></span> for the <code class="command">include "/etc/racoon/<em class="replaceable"><code>X.X.X.X</code></em>.conf"</code> statement. This statement (and the file it references) is generated when the <abbr class="abbrev">IPsec</abbr> tunnel is activated. For Workstation A, the <em class="replaceable"><code>X.X.X.X</code></em> in the <code class="command">include</code> statement is Workstation B's IP address. The opposite is true of Workstation B. The following shows a typical <code class="filename">racoon.conf</code> file when the <abbr class="abbrev">IPsec</abbr> connection is activated.
</div><pre class="screen"># Racoon IKE daemon configuration file.
# See 'man racoon.conf' for a description of the format and entries.
path include "/etc/racoon";
path pre_shared_key "/etc/racoon/psk.txt";
path certificate "/etc/racoon/certs";
sainfo anonymous
{
pfs_group 2;
lifetime time 1 hour ;
encryption_algorithm 3des, blowfish 448, rijndael ;
authentication_algorithm hmac_sha1, hmac_md5 ;
compression_algorithm deflate ;
}
include "/etc/racoon/X.X.X.X.conf";
</pre><div class="para">
This default <code class="filename">racoon.conf</code> file includes defined paths for <abbr class="abbrev">IPsec</abbr> configuration, pre-shared key files, and certificates. The fields in <code class="computeroutput">sainfo anonymous</code> describe the phase 2 SA between the <abbr class="abbrev">IPsec</abbr> nodes — the nature of the <abbr class="abbrev">IPsec</abbr> connection (including the supported encryption algorithms used) and the method of exchanging keys. The following list defines the fields of phase 2:
</div><div class="variablelist"><dl><dt><span class="term">sainfo anonymous</span></dt><dd><div class="para">
Denotes that SA can anonymously initialize with any peer provided that the <abbr class="abbrev">IPsec</abbr> credentials match.
</div></dd><dt><span class="term">pfs_group 2</span></dt><dd><div class="para">
Defines the Diffie-Hellman key exchange protocol, which determines the method by which the <abbr class="abbrev">IPsec</abbr> nodes establish a mutual temporary session key for the second phase of <abbr class="abbrev">IPsec</abbr> connectivity. By default, the Fedora implementation of <abbr class="abbrev">IPsec</abbr> uses group 2 (or <code class="computeroutput">modp1024</code>) of the Diffie-Hellman cryptographic key exchange groups. Group 2 uses a 1024-bit modular exponentiation that prevents attackers from decrypting previous <abbr class="abbrev">IPsec</abbr> transmissions even if a private key is compromised.
</div></dd><dt><span class="term">lifetime time 1 hour</span></dt><dd><div class="para">
This parameter specifies the lifetime of an SA and can be quantified either by time or by bytes of data. The default Fedora implementation of <abbr class="abbrev">IPsec</abbr> specifies a one hour lifetime.
</div></dd><dt><span class="term">encryption_algorithm 3des, blowfish 448, rijndael</span></dt><dd><div class="para">
Specifies the supported encryption ciphers for phase 2. Fedora supports 3DES, 448-bit Blowfish, and Rijndael (the cipher used in the <em class="firstterm">Advanced Encryption Standard</em>, or <acronym class="acronym">AES</acronym>).
</div></dd><dt><span class="term">authentication_algorithm hmac_sha1, hmac_md5</span></dt><dd><div class="para">
Lists the supported hash algorithms for authentication. Supported modes are sha1 and md5 hashed message authentication codes (HMAC).
</div></dd><dt><span class="term">compression_algorithm deflate</span></dt><dd><div class="para">
Defines the Deflate compression algorithm for IP Payload Compression (IPCOMP) support, which allows for potentially faster transmission of IP datagrams over slow connections.
</div></dd></dl></div><div class="para">
To start the connection, use the following command on each host:
</div><pre class="screen">[root@myServer ~]# /sbin/ifup <nickname>
</pre><div class="para">
where <nickname> is the name you specified for the <abbr class="abbrev">IPsec</abbr> connection.
</div><div class="para">
To test the <abbr class="abbrev">IPsec</abbr> connection, run the <code class="command">tcpdump</code> utility to view the network packets being transfered between the hosts and verify that they are encrypted via IPsec. The packet should include an AH header and should be shown as ESP packets. ESP means it is encrypted. For example:
</div><pre class="screen">[root@myServer ~]# tcpdump -n -i eth0 host <targetSystem>
IP 172.16.45.107 > 172.16.44.192: AH(spi=0x0954ccb6,seq=0xbb): ESP(spi=0x0c9f2164,seq=0xbb)
</pre></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec_Host_to_Host_Configuration.html"><strong>Prev</strong>2.7.6. IPsec Host-to-Host Configuration</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec_Network_to_Network_Configuration.html"><strong>Next</strong>2.7.7. IPsec Network-to-Network Configuration</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.7.7.2. Manual IPsec Network-to-Network Configuration</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec_Network_to_Network_Configuration.html" title="2.7.7. IPsec Network-to-Network Configuration"/><link rel="prev" href="sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec_Network_to_Network_Configuration.html" title="2.7.7. IPsec Network-to-Network Configuration"/><link rel="next" href="sect-Security_Guide-Virtual_Private_Networks_VPNs-Starting_and_Stopping_an_IPsec_Connection.html" title="2.7.8. Starting and Stopping an IPsec Connection"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><im
g src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec_Network_to_Network_Configuration.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Virtual_Private_Networks_VPNs-Starting_and_Stopping_an_IPsec_Connection.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-IPsec_Network_to_Network_Configuration-Manual_IPsec_Network_to_Network_Configuration">2.7.7.2. Manual <abbr class="abbrev">IPsec</abbr> Network-to-Network Configuration</h4></div></div></div><div class="para">
Suppose <acronym class="acronym">LAN</acronym> A (lana.example.com) and <acronym class="acronym">LAN</acronym> B (lanb.example.com) want to connect to each other through an <abbr class="abbrev">IPsec</abbr> tunnel. The network address for <acronym class="acronym">LAN</acronym> A is in the 192.168.1.0/24 range, while <acronym class="acronym">LAN</acronym> B uses the 192.168.2.0/24 range. The gateway IP address is 192.168.1.254 for <acronym class="acronym">LAN</acronym> A and 192.168.2.254 for <acronym class="acronym">LAN</acronym> B. The <abbr class="abbrev">IPsec</abbr> routers are separate from each <acronym class="acronym">LAN</acronym> gateway and use two network devices: eth0 is assigned to an externally-accessible static IP address which accesses the Internet, while eth1 acts as a routing point to process and transmit <acronym class="acronym">LAN</acronym> packets from one network node to the remote network nodes.
</div><div class="para">
The <abbr class="abbrev">IPsec</abbr> connection between each network uses a pre-shared key with the value of <code class="computeroutput">r3dh4tl1nux</code>, and the administrators of A and B agree to let <code class="command">racoon</code> automatically generate and share an authentication key between each <abbr class="abbrev">IPsec</abbr> router. The administrator of <acronym class="acronym">LAN</acronym> A decides to name the <abbr class="abbrev">IPsec</abbr> connection <code class="computeroutput">ipsec0</code>, while the administrator of <acronym class="acronym">LAN</acronym> B names the <abbr class="abbrev">IPsec</abbr> connection <code class="computeroutput">ipsec1</code>.
</div><div class="para">
The following example shows the contents of the <code class="filename">ifcfg</code> file for a network-to-network <abbr class="abbrev">IPsec</abbr> connection for <acronym class="acronym">LAN</acronym> A. The unique name to identify the connection in this example is <em class="replaceable"><code>ipsec0</code></em>, so the resulting file is called <code class="filename">/etc/sysconfig/network-scripts/ifcfg-ipsec0</code>.
</div><pre class="screen">TYPE=IPSEC
ONBOOT=yes
IKE_METHOD=PSK
SRCGW=192.168.1.254
DSTGW=192.168.2.254
SRCNET=192.168.1.0/24
DSTNET=192.168.2.0/24
DST=<em class="replaceable"><code>X.X.X.X</code></em>
</pre><div class="para">
The following list describes the contents of this file:
</div><div class="variablelist"><dl><dt><span class="term">TYPE=IPSEC</span></dt><dd><div class="para">
Specifies the type of connection.
</div></dd><dt><span class="term">ONBOOT=yes</span></dt><dd><div class="para">
Specifies that the connection should initiate on boot-up.
</div></dd><dt><span class="term">IKE_METHOD=PSK</span></dt><dd><div class="para">
Specifies that the connection uses the pre-shared key method of authentication.
</div></dd><dt><span class="term">SRCGW=192.168.1.254</span></dt><dd><div class="para">
The IP address of the source gateway. For LAN A, this is the LAN A gateway, and for LAN B, the LAN B gateway.
</div></dd><dt><span class="term">DSTGW=192.168.2.254</span></dt><dd><div class="para">
The IP address of the destination gateway. For LAN A, this is the LAN B gateway, and for LAN B, the LAN A gateway.
</div></dd><dt><span class="term">SRCNET=192.168.1.0/24</span></dt><dd><div class="para">
Specifies the source network for the <abbr class="abbrev">IPsec</abbr> connection, which in this example is the network range for LAN A.
</div></dd><dt><span class="term">DSTNET=192.168.2.0/24</span></dt><dd><div class="para">
Specifies the destination network for the <abbr class="abbrev">IPsec</abbr> connection, which in this example is the network range for <acronym class="acronym">LAN</acronym> B.
</div></dd><dt><span class="term">DST=X.X.X.X</span></dt><dd><div class="para">
The externally-accessible IP address of <acronym class="acronym">LAN</acronym> B.
</div></dd></dl></div><div class="para">
The following example is the content of the pre-shared key file called <code class="filename">/etc/sysconfig/network-scripts/keys-ipsec<em class="replaceable"><code>X</code></em></code> (where <em class="replaceable"><code>X</code></em> is 0 for <acronym class="acronym">LAN</acronym> A and 1 for <acronym class="acronym">LAN</acronym> B) that both networks use to authenticate each other. The contents of this file should be identical and only the root user should be able to read or write this file.
</div><pre class="screen">IKE_PSK=r3dh4tl1nux
</pre><div class="important"><h2>Important</h2><div class="para">
To change the <code class="filename">keys-ipsec<em class="replaceable"><code>X</code></em></code> file so that only the root user can read or edit the file, use the following command after creating the file:
</div><pre class="screen">chmod 600 /etc/sysconfig/network-scripts/keys-ipsec1
</pre></div><div class="para">
To change the authentication key at any time, edit the <code class="filename">keys-ipsec<em class="replaceable"><code>X</code></em></code> file on both <abbr class="abbrev">IPsec</abbr> routers. <span class="emphasis"><em>Both keys must be identical for proper connectivity</em></span>.
</div><div class="para">
The following example is the contents of the <code class="filename">/etc/racoon/racoon.conf</code> configuration file for the <abbr class="abbrev">IPsec</abbr> connection. Note that the <code class="computeroutput">include</code> line at the bottom of the file is automatically generated and only appears if the <abbr class="abbrev">IPsec</abbr> tunnel is running.
</div><pre class="screen"># Racoon IKE daemon configuration file.
# See 'man racoon.conf' for a description of the format and entries.
path include "/etc/racoon";
path pre_shared_key "/etc/racoon/psk.txt";
path certificate "/etc/racoon/certs";
sainfo anonymous
{
pfs_group 2;
lifetime time 1 hour ;
encryption_algorithm 3des, blowfish 448, rijndael ;
authentication_algorithm hmac_sha1, hmac_md5 ;
compression_algorithm deflate ;
}
include "/etc/racoon/<em class="replaceable"><code>X.X.X.X</code></em>.conf"
</pre><div class="para">
The following is the specific configuration for the connection to the remote network. The file is called <code class="filename"><em class="replaceable"><code>X.X.X.X</code></em>.conf</code> (where <em class="replaceable"><code>X.X.X.X</code></em> is the IP address of the remote <abbr class="abbrev">IPsec</abbr> router). Note that this file is automatically generated when the <abbr class="abbrev">IPsec</abbr> tunnel is activated and should not be edited directly.
</div><pre class="screen">remote <em class="replaceable"><code>X.X.X.X</code></em>{
exchange_mode aggressive, main;
my_identifier address;
proposal {
encryption_algorithm 3des;
hash_algorithm sha1;
authentication_method pre_shared_key;
dh_group 2 ;
}
}
</pre><div class="para">
Prior to starting the <abbr class="abbrev">IPsec</abbr> connection, IP forwarding should be enabled in the kernel. To enable IP forwarding:
</div><div class="orderedlist"><ol><li><div class="para">
Edit <code class="filename">/etc/sysctl.conf</code> and set <code class="computeroutput">net.ipv4.ip_forward</code> to <strong class="userinput"><code>1</code></strong>.
</div></li><li><div class="para">
Use the following command to enable the change:
</div><pre class="screen">[root@myServer ~] # sysctl -p /etc/sysctl.conf
</pre></li></ol></div><div class="para">
To start the <abbr class="abbrev">IPsec</abbr> connection, use the following command on each router:
</div><pre class="screen">[root@myServer ~] # /sbin/ifup ipsec0
</pre><div class="para">
The connections are activated, and both <acronym class="acronym">LAN</acronym> A and <acronym class="acronym">LAN</acronym> B are able to communicate with each other. The routes are created automatically via the initialization script called by running <code class="command">ifup</code> on the <abbr class="abbrev">IPsec</abbr> connection. To show a list of routes for the network, use the following command:
</div><pre class="screen">[root@myServer ~] # /sbin/ip route list
</pre><div class="para">
To test the <abbr class="abbrev">IPsec</abbr> connection, run the <code class="command">tcpdump</code> utility on the externally-routable device (eth0 in this example) to view the network packets being transfered between the hosts (or networks), and verify that they are encrypted via IPsec. For example, to check the <abbr class="abbrev">IPsec</abbr> connectivity of <acronym class="acronym">LAN</acronym> A, use the following command:
</div><pre class="screen">[root@myServer ~] # tcpdump -n -i eth0 host <em class="replaceable"><code>lana.example.com</code></em>
</pre><div class="para">
The packet should include an AH header and should be shown as ESP packets. ESP means it is encrypted. For example (back slashes denote a continuation of one line):
</div><pre class="screen">12:24:26.155529 lanb.example.com > lana.example.com: AH(spi=0x021c9834,seq=0x358): \
lanb.example.com > lana.example.com: ESP(spi=0x00c887ad,seq=0x358) (DF) \
(ipip-proto-4)
</pre></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Virtual_Private_Networks_VPNs-IPsec_Network_to_Network_Configuration.html"><strong>Prev</strong>2.7.7. IPsec Network-to-Network Configuration</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Virtual_Private_Networks_VPNs-Starting_and_Stopping_an_IPsec_Connection.html"><strong>Next</strong>2.7.8. Starting and Stopping an IPsec Connection</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.6.10. Additional Resources</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Kerberos.html" title="2.6. Kerberos"/><link rel="prev" href="sect-Security_Guide-Kerberos-Setting_Up_Cross_Realm_Authentication.html" title="2.6.9. Setting Up Cross Realm Authentication"/><link rel="next" href="sect-Security_Guide-Additional_Resources-Useful_Kerberos_Websites.html" title="2.6.10.2. Useful Kerberos Websites"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Docu
mentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Kerberos-Setting_Up_Cross_Realm_Authentication.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Additional_Resources-Useful_Kerberos_Websites.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Kerberos-Additional_Resources">2.6.10. Additional Resources</h3></div></div></div><a id="d0e10726" class="indexterm"/><div class="para">
For more information about Kerberos, refer to the following resources.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Additional_Resources-Installed_Kerberos_Documentation">2.6.10.1. Installed Kerberos Documentation</h4></div></div></div><a id="d0e10736" class="indexterm"/><div class="itemizedlist"><ul><li><div class="para">
The <em class="citetitle">Kerberos V5 Installation Guide</em> and the <em class="citetitle">Kerberos V5 System Administrator's Guide</em> in PostScript and HTML formats. These can be found in the <code class="filename">/usr/share/doc/krb5-server-<em class="replaceable"><code><version-number></code></em>/</code> directory (where <em class="replaceable"><code><version-number></code></em> is the version number of the <code class="command">krb5-server</code> package installed on your system).
</div></li><li><div class="para">
The <em class="citetitle">Kerberos V5 UNIX User's Guide</em> in PostScript and HTML formats. These can be found in the <code class="filename">/usr/share/doc/krb5-workstation-<em class="replaceable"><code><version-number></code></em>/</code> directory (where <em class="replaceable"><code><version-number></code></em> is the version number of the <code class="command">krb5-workstation</code> package installed on your system).
</div></li><li><div class="para">
Kerberos man pages — There are a number of man pages for the various applications and configuration files involved with a Kerberos implementation. The following is a list of some of the more important man pages.
</div><div class="variablelist"><dl><dt><span class="term">Client Applications</span></dt><dd><div class="itemizedlist"><ul><li><div class="para">
<code class="command">man kerberos</code> — An introduction to the Kerberos system which describes how credentials work and provides recommendations for obtaining and destroying Kerberos tickets. The bottom of the man page references a number of related man pages.
</div></li><li><div class="para">
<code class="command">man kinit</code> — Describes how to use this command to obtain and cache a ticket-granting ticket.
</div></li><li><div class="para">
<code class="command">man kdestroy</code> — Describes how to use this command to destroy Kerberos credentials.
</div></li><li><div class="para">
<code class="command">man klist</code> — Describes how to use this command to list cached Kerberos credentials.
</div></li></ul></div></dd><dt><span class="term">Administrative Applications</span></dt><dd><div class="itemizedlist"><ul><li><div class="para">
<code class="command">man kadmin</code> — Describes how to use this command to administer the Kerberos V5 database.
</div></li><li><div class="para">
<code class="command">man kdb5_util</code> — Describes how to use this command to create and perform low-level administrative functions on the Kerberos V5 database.
</div></li></ul></div></dd><dt><span class="term">Server Applications</span></dt><dd><div class="itemizedlist"><ul><li><div class="para">
<code class="command">man krb5kdc</code> — Describes available command line options for the Kerberos V5 KDC.
</div></li><li><div class="para">
<code class="command">man kadmind</code> — Describes available command line options for the Kerberos V5 administration server.
</div></li></ul></div></dd><dt><span class="term">Configuration Files</span></dt><dd><div class="itemizedlist"><ul><li><div class="para">
<code class="command">man krb5.conf</code> — Describes the format and options available within the configuration file for the Kerberos V5 library.
</div></li><li><div class="para">
<code class="command">man kdc.conf</code> — Describes the format and options available within the configuration file for the Kerberos V5 AS and KDC.
</div></li></ul></div></dd></dl></div></li></ul></div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Kerberos-Setting_Up_Cross_Realm_Authentication.html"><strong>Prev</strong>2.6.9. Setting Up Cross Realm Authentication</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Additional_Resources-Useful_Kerberos_Websites.html"><strong>Next</strong>2.6.10.2. Useful Kerberos Websites</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.6.6. Configuring a Kerberos 5 Client</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Kerberos.html" title="2.6. Kerberos"/><link rel="prev" href="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Server.html" title="2.6.5. Configuring a Kerberos 5 Server"/><link rel="next" href="sect-Security_Guide-Kerberos-Domain_to_Realm_Mapping.html" title="2.6.7. Domain-to-Realm Mapping"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></
a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Server.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos-Domain_to_Realm_Mapping.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Client">2.6.6. Configuring a Kerberos 5 Client</h3></div></div></div><a id="d0e9792" class="indexterm"/><div class="para">
Setting up a Kerberos 5 client is less involved than setting up a server. At a minimum, install the client packages and provide each client with a valid <code class="filename">krb5.conf</code> configuration file. While <code class="command">ssh</code> and <code class="command">slogin</code> are the preferred method of remotely logging in to client systems, Kerberized versions of <code class="command">rsh</code> and <code class="command">rlogin</code> are still available, though deploying them requires that a few more configuration changes be made.
</div><div class="procedure"><ol class="1"><li><div class="para">
Be sure that time synchronization is in place between the Kerberos client and the KDC. Refer to <a class="xref" href="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Server.html" title="2.6.5. Configuring a Kerberos 5 Server">Section 2.6.5, “Configuring a Kerberos 5 Server”</a> for more information. In addition, verify that DNS is working properly on the Kerberos client before configuring the Kerberos client programs.
</div></li><li><div class="para">
Install the <code class="filename">krb5-libs</code> and <code class="filename">krb5-workstation</code> packages on all of the client machines. Supply a valid <code class="filename">/etc/krb5.conf</code> file for each client (usually this can be the same <code class="filename">krb5.conf</code> file used by the KDC).
</div></li><li><div class="para">
Before a workstation in the realm can use Kerberos to authenticate users who connect using <code class="command">ssh</code> or Kerberized <code class="command">rsh</code> or <code class="command">rlogin</code>, it must have its own host principal in the Kerberos database. The <code class="command">sshd</code>, <code class="command">kshd</code>, and <code class="command">klogind</code> server programs all need access to the keys for the <span class="emphasis"><em>host</em></span> service's principal. Additionally, in order to use the kerberized <code class="command">rsh</code> and <code class="command">rlogin</code> services, that workstation must have the <code class="filename">xinetd</code> package installed.
</div><div class="para">
Using <code class="command">kadmin</code>, add a host principal for the workstation on the KDC. The instance in this case is the hostname of the workstation. Use the <code class="command">-randkey</code> option for the <code class="command">kadmin</code>'s <code class="command">addprinc</code> command to create the principal and assign it a random key:
</div><pre class="screen">addprinc -randkey host/<em class="replaceable"><code>blah.example.com</code></em>
</pre><div class="para">
Now that the principal has been created, keys can be extracted for the workstation by running <code class="command">kadmin</code> <span class="emphasis"><em>on the workstation itself</em></span>, and using the <code class="command">ktadd</code> command within <code class="command">kadmin</code>:
</div><pre class="screen">ktadd -k /etc/krb5.keytab host/<em class="replaceable"><code>blah.example.com</code></em>
</pre></li><li><div class="para">
To use other kerberized network services, they must first be started. Below is a list of some common kerberized services and instructions about enabling them:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="command">ssh</code> — OpenSSH uses GSS-API to authenticate users to servers if the client's and server's configuration both have <code class="option">GSSAPIAuthentication</code> enabled. If the client also has <code class="option">GSSAPIDelegateCredentials</code> enabled, the user's credentials are made available on the remote system.
</div></li><li><div class="para">
<code class="command">rsh</code> and <code class="command">rlogin</code> — To use the kerberized versions of <code class="command">rsh</code> and <code class="command">rlogin</code>, enable <code class="command">klogin</code>, <code class="command">eklogin</code>, and <code class="command">kshell</code>.
</div></li><li><div class="para">
Telnet — To use kerberized Telnet, <code class="command">krb5-telnet</code> must be enabled.
</div></li><li><div class="para">
FTP — To provide FTP access, create and extract a key for the principal with a root of <code class="computeroutput">ftp</code>. Be certain to set the instance to the fully qualified hostname of the FTP server, then enable <code class="command">gssftp</code>.
</div></li><li><div class="para">
IMAP — To use a kerberized IMAP server, the <code class="filename">cyrus-imap</code> package uses Kerberos 5 if it also has the <code class="filename">cyrus-sasl-gssapi</code> package installed. The <code class="filename">cyrus-sasl-gssapi</code> package contains the Cyrus SASL plugins which support GSS-API authentication. Cyrus IMAP should function properly with Kerberos as long as the <code class="command">cyrus</code> user is able to find the proper key in <code class="filename">/etc/krb5.keytab</code>, and the root for the principal is set to <code class="command">imap</code> (created with <code class="command">kadmin</code>).
</div><div class="para">
An alternative to <code class="filename">cyrus-imap</code> can be found in the <code class="command">dovecot</code> package, which is also included in Fedora. This package contains an IMAP server but does not, to date, support GSS-API and Kerberos.
</div></li><li><div class="para">
CVS — To use a kerberized CVS server, <code class="command">gserver</code> uses a principal with a root of <code class="computeroutput">cvs</code> and is otherwise identical to the CVS <code class="command">pserver</code>.
</div></li></ul></div></li></ol></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Server.html"><strong>Prev</strong>2.6.5. Configuring a Kerberos 5 Server</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos-Domain_to_Realm_Mapping.html"><strong>Next</strong>2.6.7. Domain-to-Realm Mapping</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.6.5. Configuring a Kerberos 5 Server</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Kerberos.html" title="2.6. Kerberos"/><link rel="prev" href="sect-Security_Guide-Kerberos-Kerberos_and_PAM.html" title="2.6.4. Kerberos and PAM"/><link rel="next" href="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Client.html" title="2.6.6. Configuring a Kerberos 5 Client"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul clas
s="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Kerberos-Kerberos_and_PAM.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Client.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Server">2.6.5. Configuring a Kerberos 5 Server</h3></div></div></div><a id="d0e9582" class="indexterm"/><div class="para">
When setting up Kerberos, install the KDC first. If it is necessary to set up slave servers, install the master first.
</div><div class="para">
To configure the first Kerberos KDC, follow these steps:
</div><div class="procedure"><ol class="1"><li><div class="para">
Ensure that time synchronization and DNS are functioning correctly on all client and server machines before configuring Kerberos. Pay particular attention to time synchronization between the Kerberos server and its clients. If the time difference between the server and client is greater than five minutes (this is configurable in Kerberos 5), Kerberos clients can not authenticate to the server. This time synchronization is necessary to prevent an attacker from using an old Kerberos ticket to masquerade as a valid user.
</div><div class="para">
It is advisable to set up a Network Time Protocol (NTP) compatible client/server network even if Kerberos is not being used. Fedora includes the <code class="filename">ntp</code> package for this purpose. Refer to <code class="filename">/usr/share/doc/ntp-<em class="replaceable"><code><version-number></code></em>/index.html</code> (where <em class="replaceable"><code><version-number></code></em> is the version number of the <code class="filename">ntp</code> package installed on your system) for details about how to set up Network Time Protocol servers, and <a href="http://www.ntp.org">http://www.ntp.org</a> for more information about NTP.
</div></li><li><div class="para">
Install the <code class="filename">krb5-libs</code>, <code class="filename">krb5-server</code>, and <code class="filename">krb5-workstation</code> packages on the dedicated machine which runs the KDC. This machine needs to be very secure — if possible, it should not run any services other than the KDC.
</div></li><li><div class="para">
Edit the <code class="filename">/etc/krb5.conf</code> and <code class="filename">/var/kerberos/krb5kdc/kdc.conf</code> configuration files to reflect the realm name and domain-to-realm mappings. A simple realm can be constructed by replacing instances of <em class="replaceable"><code>EXAMPLE.COM</code></em> and <em class="replaceable"><code>example.com</code></em> with the correct domain name — being certain to keep uppercase and lowercase names in the correct format — and by changing the KDC from <em class="replaceable"><code>kerberos.example.com</code></em> to the name of the Kerberos server. By convention, all realm names are uppercase and all DNS hostnames and domain names are lowercase. For full details about the formats of these configuration files, refer to their respective man pages.
</div></li><li><div class="para">
Create the database using the <code class="command">kdb5_util</code> utility from a shell prompt:
</div><pre class="screen">/usr/kerberos/sbin/kdb5_util create -s
</pre><div class="para">
The <code class="command">create</code> command creates the database that stores keys for the Kerberos realm. The <code class="command">-s</code> switch forces creation of a <em class="firstterm">stash</em> file in which the master server key is stored. If no stash file is present from which to read the key, the Kerberos server (<code class="command">krb5kdc</code>) prompts the user for the master server password (which can be used to regenerate the key) every time it starts.
</div></li><li><div class="para">
Edit the <code class="filename">/var/kerberos/krb5kdc/kadm5.acl</code> file. This file is used by <code class="command">kadmind</code> to determine which principals have administrative access to the Kerberos database and their level of access. Most organizations can get by with a single line:
</div><pre class="screen">*/admin(a)EXAMPLE.com *
</pre><div class="para">
Most users are represented in the database by a single principal (with a <span class="emphasis"><em>NULL</em></span>, or empty, instance, such as <span class="emphasis"><em>joe(a)EXAMPLE.COM</em></span>). In this configuration, users with a second principal with an instance of <span class="emphasis"><em>admin</em></span> (for example, <span class="emphasis"><em>joe/admin(a)EXAMPLE.COM</em></span>) are able to wield full power over the realm's Kerberos database.
</div><div class="para">
After <code class="command">kadmind</code> has been started on the server, any user can access its services by running <code class="command">kadmin</code> on any of the clients or servers in the realm. However, only users listed in the <code class="filename">kadm5.acl</code> file can modify the database in any way, except for changing their own passwords.
</div><div class="note"><h2>Note</h2><div class="para">
The <code class="command">kadmin</code> utility communicates with the <code class="command">kadmind</code> server over the network, and uses Kerberos to handle authentication. Consequently, the first principal must already exist before connecting to the server over the network to administer it. Create the first principal with the <code class="command">kadmin.local</code> command, which is specifically designed to be used on the same host as the KDC and does not use Kerberos for authentication.
</div></div><div class="para">
Type the following <code class="command">kadmin.local</code> command at the KDC terminal to create the first principal:
</div><pre class="screen">/usr/kerberos/sbin/kadmin.local -q "addprinc <em class="replaceable"><code>username</code></em>/admin"
</pre></li><li><div class="para">
Start Kerberos using the following commands:
</div><pre class="screen">/sbin/service krb5kdc start
/sbin/service kadmin start
/sbin/service krb524 start
</pre></li><li><div class="para">
Add principals for the users using the <code class="command">addprinc</code> command within <code class="command">kadmin</code>. <code class="command">kadmin</code> and <code class="command">kadmin.local</code> are command line interfaces to the KDC. As such, many commands — such as <code class="command">addprinc</code> — are available after launching the <code class="command">kadmin</code> program. Refer to the <code class="command">kadmin</code> man page for more information.
</div></li><li><div class="para">
Verify that the KDC is issuing tickets. First, run <code class="command">kinit</code> to obtain a ticket and store it in a credential cache file. Next, use <code class="command">klist</code> to view the list of credentials in the cache and use <code class="command">kdestroy</code> to destroy the cache and the credentials it contains.
</div><div class="note"><h2>Note</h2><div class="para">
By default, <code class="command">kinit</code> attempts to authenticate using the same system login username (not the Kerberos server). If that username does not correspond to a principal in the Kerberos database, <code class="command">kinit</code> issues an error message. If that happens, supply <code class="command">kinit</code> with the name of the correct principal as an argument on the command line (<code class="command">kinit <em class="replaceable"><code><principal></code></em></code>).
</div></div></li></ol></div><div class="para">
Once these steps are completed, the Kerberos server should be up and running.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Kerberos-Kerberos_and_PAM.html"><strong>Prev</strong>2.6.4. Kerberos and PAM</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Client.html"><strong>Next</strong>2.6.6. Configuring a Kerberos 5 Client</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.6.7. Domain-to-Realm Mapping</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Kerberos.html" title="2.6. Kerberos"/><link rel="prev" href="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Client.html" title="2.6.6. Configuring a Kerberos 5 Client"/><link rel="next" href="sect-Security_Guide-Kerberos-Setting_Up_Secondary_KDCs.html" title="2.6.8. Setting Up Secondary KDCs"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></
p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Client.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos-Setting_Up_Secondary_KDCs.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Kerberos-Domain_to_Realm_Mapping">2.6.7. Domain-to-Realm Mapping</h3></div></div></div><div class="para">
When a client attempts to access a service running on a particular server, it knows the name of the service (<span class="emphasis"><em>host</em></span>) and the name of the server (<span class="emphasis"><em>foo.example.com</em></span>), but because more than one realm may be deployed on your network, it must guess at the name of the realm in which the service resides.
</div><div class="para">
By default, the name of the realm is taken to be the DNS domain name of the server, upper-cased.
</div><div class="literallayout"><p>foo.example.org → EXAMPLE.ORG<br/>
foo.example.com → EXAMPLE.COM<br/>
foo.hq.example.com → HQ.EXAMPLE.COM<br/>
</p></div><div class="para">
In some configurations, this will be sufficient, but in others, the realm name which is derived will be the name of a non-existant realm. In these cases, the mapping from the server's DNS domain name to the name of its realm must be specified in the <span class="emphasis"><em>domain_realm</em></span> section of the client system's <code class="filename">krb5.conf</code>. For example:
</div><pre class="screen">[domain_realm]
.example.com = EXAMPLE.COM
example.com = EXAMPLE.COM
</pre><div class="para">
The above configuration specifies two mappings. The first mapping specifies that any system in the "example.com" DNS domain belongs to the <span class="emphasis"><em>EXAMPLE.COM</em></span> realm. The second specifies that a system with the exact name "example.com" is also in the realm. (The distinction between a domain and a specific host is marked by the presence or lack of an initial ".".) The mapping can also be stored directly in DNS.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Client.html"><strong>Prev</strong>2.6.6. Configuring a Kerberos 5 Client</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos-Setting_Up_Secondary_KDCs.html"><strong>Next</strong>2.6.8. Setting Up Secondary KDCs</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.6.3. How Kerberos Works</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Kerberos.html" title="2.6. Kerberos"/><link rel="prev" href="sect-Security_Guide-Kerberos-Kerberos_Terminology.html" title="2.6.2. Kerberos Terminology"/><link rel="next" href="sect-Security_Guide-Kerberos-Kerberos_and_PAM.html" title="2.6.4. Kerberos and PAM"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a
accesskey="p" href="sect-Security_Guide-Kerberos-Kerberos_Terminology.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos-Kerberos_and_PAM.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Kerberos-How_Kerberos_Works">2.6.3. How Kerberos Works</h3></div></div></div><a id="d0e9443" class="indexterm"/><a id="d0e9448" class="indexterm"/><a id="d0e9453" class="indexterm"/><a id="d0e9458" class="indexterm"/><a id="d0e9463" class="indexterm"/><div class="para">
Kerberos differs from username/password authentication methods. Instead of authenticating each user to each network service, Kerberos uses symmetric encryption and a trusted third party (a KDC), to authenticate users to a suite of network services. When a user authenticates to the KDC, the KDC sends a ticket specific to that session back to the user's machine, and any Kerberos-aware services look for the ticket on the user's machine rather than requiring the user to authenticate using a password.
</div><div class="para">
When a user on a Kerberos-aware network logs in to their workstation, their principal is sent to the KDC as part of a request for a TGT from the Authentication Server. This request can be sent by the log-in program so that it is transparent to the user, or can be sent by the <code class="command">kinit</code> program after the user logs in.
</div><div class="para">
The KDC then checks for the principal in its database. If the principal is found, the KDC creates a TGT, which is encrypted using the user's key and returned to that user.
</div><div class="para">
The login or <code class="command">kinit</code> program on the client then decrypts the TGT using the user's key, which it computes from the user's password. The user's key is used only on the client machine and is <span class="emphasis"><em>not</em></span> transmitted over the network.
</div><div class="para">
The TGT is set to expire after a certain period of time (usually ten to twenty-four hours) and is stored in the client machine's credentials cache. An expiration time is set so that a compromised TGT is of use to an attacker for only a short period of time. After the TGT has been issued, the user does not have to re-enter their password until the TGT expires or until they log out and log in again.
</div><div class="para">
Whenever the user needs access to a network service, the client software uses the TGT to request a new ticket for that specific service from the TGS. The service ticket is then used to authenticate the user to that service transparently.
</div><div class="warning"><h2>Warning</h2><div class="para">
The Kerberos system can be compromised if a user on the network authenticates against a non-Kerberos aware service by transmitting a password in plain text. The use of non-Kerberos aware services is highly discouraged. Such services include Telnet and FTP. The use of other encrypted protocols, such as SSH or SSL-secured services, however, is preferred, although not ideal.
</div></div><div class="para">
This is only a broad overview of how Kerberos authentication works. Refer to <a class="xref" href="sect-Security_Guide-Kerberos-Additional_Resources.html" title="2.6.10. Additional Resources">Section 2.6.10, “Additional Resources”</a> for links to more in-depth information.
</div><div class="note"><h2>Note</h2><div class="para">
Kerberos depends on the following network services to function correctly.
<div class="itemizedlist"><ul><li><div class="para">
Approximate clock synchronization between the machines on the network.
</div><div class="para">
A clock synchronization program should be set up for the network, such as <code class="command">ntpd</code>. Refer to <code class="filename">/usr/share/doc/ntp-<em class="replaceable"><code><version-number></code></em>/index.html</code> for details on setting up Network Time Protocol servers (where <em class="replaceable"><code><version-number></code></em> is the version number of the <code class="filename">ntp</code> package installed on your system).
</div></li><li><div class="para">
Domain Name Service (DNS).
</div><div class="para">
You should ensure that the DNS entries and hosts on the network are all properly configured. Refer to the <em class="citetitle">Kerberos V5 System Administrator's Guide</em> in <code class="filename">/usr/share/doc/krb5-server-<em class="replaceable"><code><version-number></code></em></code> for more information (where <em class="replaceable"><code><version-number></code></em> is the version number of the <code class="filename">krb5-server</code> package installed on your system).
</div></li></ul></div>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.6.2. Kerberos Terminology</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Kerberos.html" title="2.6. Kerberos"/><link rel="prev" href="sect-Security_Guide-Kerberos.html" title="2.6. Kerberos"/><link rel="next" href="sect-Security_Guide-Kerberos-How_Kerberos_Works.html" title="2.6.3. How Kerberos Works"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Secu
rity_Guide-Kerberos.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos-How_Kerberos_Works.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Kerberos-Kerberos_Terminology">2.6.2. Kerberos Terminology</h3></div></div></div><a id="d0e9276" class="indexterm"/><div class="para">
Kerberos has its own terminology to define various aspects of the service. Before learning how Kerberos works, it is important to learn the following terms.
</div><div class="variablelist"><dl><dt><span class="term">authentication server (AS)</span></dt><dd><div class="para">
A server that issues tickets for a desired service which are in turn given to users for access to the service. The AS responds to requests from clients who do not have or do not send credentials with a request. It is usually used to gain access to the ticket-granting server (TGS) service by issuing a ticket-granting ticket (TGT). The AS usually runs on the same host as the key distribution center (KDC).
</div></dd><dt><span class="term">ciphertext</span></dt><dd><div class="para">
Encrypted data.
</div></dd><dt><span class="term">client</span></dt><dd><div class="para">
An entity on the network (a user, a host, or an application) that can receive a ticket from Kerberos.
</div></dd><dt><span class="term">credentials</span></dt><dd><div class="para">
A temporary set of electronic credentials that verify the identity of a client for a particular service. Also called a ticket.
</div></dd><dt><span class="term">credential cache or ticket file</span></dt><dd><div class="para">
A file which contains the keys for encrypting communications between a user and various network services. Kerberos 5 supports a framework for using other cache types, such as shared memory, but files are more thoroughly supported.
</div></dd><dt><span class="term">crypt hash</span></dt><dd><div class="para">
A one-way hash used to authenticate users. These are more secure than using unencrypted data, but they are still relatively easy to decrypt for an experienced cracker.
</div></dd><dt><span class="term">GSS-API</span></dt><dd><div class="para">
The Generic Security Service Application Program Interface (defined in RFC-2743 published by The Internet Engineering Task Force) is a set of functions which provide security services. This API is used by clients and services to authenticate to each other without either program having specific knowledge of the underlying mechanism. If a network service (such as cyrus-IMAP) uses GSS-API, it can authenticate using Kerberos.
</div></dd><dt><span class="term">hash</span></dt><dd><div class="para">
Also known as a <em class="firstterm">hash value</em>. A value generated by passing a string through a <em class="firstterm">hash function</em>. These values are typically used to ensure that transmitted data has not been tampered with.
</div></dd><dt><span class="term">hash function</span></dt><dd><div class="para">
A way of generating a digital "fingerprint" from input data. These functions rearrange, transpose or otherwise alter data to produce a <em class="firstterm">hash value</em>.
</div></dd><dt><span class="term">key</span></dt><dd><div class="para">
Data used when encrypting or decrypting other data. Encrypted data cannot be decrypted without the proper key or extremely good fortune on the part of the cracker.
</div></dd><dt><span class="term">key distribution center (KDC)</span></dt><dd><div class="para">
A service that issues Kerberos tickets, and which usually run on the same host as the ticket-granting server (TGS).
</div></dd><dt><span class="term">keytab (or key table)</span></dt><dd><div class="para">
A file that includes an unencrypted list of principals and their keys. Servers retrieve the keys they need from keytab files instead of using <code class="command">kinit</code>. The default keytab file is <code class="filename">/etc/krb5.keytab</code>. The KDC administration server, <code class="command">/usr/kerberos/sbin/kadmind</code>, is the only service that uses any other file (it uses <code class="filename">/var/kerberos/krb5kdc/kadm5.keytab</code>).
</div></dd><dt><span class="term">kinit</span></dt><dd><div class="para">
The <code class="command">kinit</code> command allows a principal who has already logged in to obtain and cache the initial ticket-granting ticket (TGT). Refer to the <code class="command">kinit</code> man page for more information.
</div></dd><dt><span class="term">principal (or principal name)</span></dt><dd><div class="para">
The principal is the unique name of a user or service allowed to authenticate using Kerberos. A principal follows the form <code class="computeroutput">root[/instance]@REALM</code>. For a typical user, the root is the same as their login ID. The <code class="computeroutput">instance</code> is optional. If the principal has an instance, it is separated from the root with a forward slash ("/"). An empty string ("") is considered a valid instance (which differs from the default <code class="computeroutput">NULL</code> instance), but using it can be confusing. All principals in a realm have their own key, which for users is derived from a password or is randomly set for services.
</div></dd><dt><span class="term">realm</span></dt><dd><div class="para">
A network that uses Kerberos, composed of one or more servers called KDCs and a potentially large number of clients.
</div></dd><dt><span class="term">service</span></dt><dd><div class="para">
A program accessed over the network.
</div></dd><dt><span class="term">ticket</span></dt><dd><div class="para">
A temporary set of electronic credentials that verify the identity of a client for a particular service. Also called credentials.
</div></dd><dt><span class="term">ticket-granting server (TGS)</span></dt><dd><div class="para">
A server that issues tickets for a desired service which are in turn given to users for access to the service. The TGS usually runs on the same host as the KDC.
</div></dd><dt><span class="term">ticket-granting ticket (TGT)</span></dt><dd><div class="para">
A special ticket that allows the client to obtain additional tickets without applying for them from the KDC.
</div></dd><dt><span class="term">unencrypted password</span></dt><dd><div class="para">
A plain text, human-readable password.
</div></dd></dl></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Kerberos.html"><strong>Prev</strong>2.6. Kerberos</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos-How_Kerberos_Works.html"><strong>Next</strong>2.6.3. How Kerberos Works</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.6.4. Kerberos and PAM</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Kerberos.html" title="2.6. Kerberos"/><link rel="prev" href="sect-Security_Guide-Kerberos-How_Kerberos_Works.html" title="2.6.3. How Kerberos Works"/><link rel="next" href="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Server.html" title="2.6.5. Configuring a Kerberos 5 Server"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav">
<li class="previous"><a accesskey="p" href="sect-Security_Guide-Kerberos-How_Kerberos_Works.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos-Configuring_a_Kerberos_5_Server.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Kerberos-Kerberos_and_PAM">2.6.4. Kerberos and PAM</h3></div></div></div><a id="d0e9547" class="indexterm"/><a id="d0e9552" class="indexterm"/><div class="para">
Kerberos-aware services do not currently make use of Pluggable Authentication Modules (PAM) — these services bypass PAM completely. However, applications that use PAM can make use of Kerberos for authentication if the <code class="filename">pam_krb5</code> module (provided in the <code class="filename">pam_krb5</code> package) is installed. The <code class="filename">pam_krb5</code> package contains sample configuration files that allow services such as <code class="command">login</code> and <code class="command">gdm</code> to authenticate users as well as obtain initial credentials using their passwords. If access to network servers is always performed using Kerberos-aware services or services that use GSS-API, such as IMAP, the network can be considered reasonably safe.
</div><div class="tip"><h2>Tip</h2><div class="para">
Administrators should be careful not to allow users to authenticate to most network services using Kerberos passwords. Many protocols used by these services do not encrypt the password before sending it over the network, destroying the benefits of the Kerberos system. For example, users should not be allowed to authenticate to Telnet services with the same password they use for Kerberos authentication.
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.6.9. Setting Up Cross Realm Authentication</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Kerberos.html" title="2.6. Kerberos"/><link rel="prev" href="sect-Security_Guide-Kerberos-Setting_Up_Secondary_KDCs.html" title="2.6.8. Setting Up Secondary KDCs"/><link rel="next" href="sect-Security_Guide-Kerberos-Additional_Resources.html" title="2.6.10. Additional Resources"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul c
lass="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Kerberos-Setting_Up_Secondary_KDCs.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos-Additional_Resources.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Kerberos-Setting_Up_Cross_Realm_Authentication">2.6.9. Setting Up Cross Realm Authentication</h3></div></div></div><div class="para">
<span class="emphasis"><em>Cross-realm authentication</em></span> is the term which is used to describe situations in which clients (typically users) of one realm use Kerberos to authenticate to services (typically server processes running on a particular server system) which belong to a realm other than their own.
</div><div class="para">
For the simplest case, in order for a client of a realm named <code class="literal">A.EXAMPLE.COM</code> to access a service in the <code class="literal">B.EXAMPLE.COM</code> realm, both realms must share a key for a principal named <code class="literal">krbtgt/B.EXAMPLE.COM(a)A.EXAMPLE.COM</code>, and both keys must have the same key version number associated with them.
</div><div class="para">
To accomplish this, select a very strong password or passphrase, and create an entry for the principal in both realms using kadmin.
</div><div class="literallayout"><p> <code class="computeroutput"><code class="prompt">#</code> <strong class="userinput"><code>kadmin -r A.EXAMPLE.COM</code></strong></code> <code class="computeroutput"><code class="prompt">kadmin:</code> <strong class="userinput"><code>add_principal krbtgt/B.EXAMPLE.COM(a)A.EXAMPLE.COM</code></strong></code> <code class="computeroutput">Enter password for principal "krbtgt/B.EXAMPLE.COM(a)A.EXAMPLE.COM":</code> <code class="computeroutput">Re-enter password for principal "krbtgt/B.EXAMPLE.COM(a)A.EXAMPLE.COM":</code> <code class="computeroutput">Principal "krbtgt/B.EXAMPLE.COM(a)A.EXAMPLE.COM" created.</code> <strong class="userinput"><code>quit</code></strong> <code class="computeroutput"><code class="prompt">#</code> <strong class="userinput"><code>kadmin -r B.EXAMPLE.COM</code></strong></code> <code class="computeroutput"><code class="prompt">kadmin:</code> <strong class="userinput"><code>add_principal krbtgt/B.EXAM
PLE.COM(a)A.EXAMPLE.COM</code></strong></code> <code class="computeroutput">Enter password for principal "krbtgt/B.EXAMPLE.COM(a)A.EXAMPLE.COM":</code> <code class="computeroutput">Re-enter password for principal "krbtgt/B.EXAMPLE.COM(a)A.EXAMPLE.COM":</code> <code class="computeroutput">Principal "krbtgt/B.EXAMPLE.COM(a)A.EXAMPLE.COM" created.</code> <strong class="userinput"><code>quit</code></strong><br/>
</p></div><div class="para">
Use the <code class="command">get_principal</code> command to verify that both entries have matching key version numbers (<code class="literal">kvno</code> values) and encryption types.
</div><div class="caution"><h2>Dumping the Database Doesn't Do It</h2><div class="para">
Security-conscious administrators may attempt to use the <code class="command">add_principal</code> command's <code class="literal">-randkey</code> option to assign a random key instead of a password, dump the new entry from the database of the first realm, and import it into the second. This will not work unless the master keys for the realm databases are identical, as the keys contained in a database dump are themselves encrypted using the master key.
</div></div><div class="para">
Clients in the <code class="literal">A.EXAMPLE.COM</code> realm are now able to authenticate to services in the <code class="literal">B.EXAMPLE.COM</code> realm. Put another way, the <code class="literal">B.EXAMPLE.COM</code> realm now <span class="emphasis"><em>trusts</em></span> the <code class="literal">A.EXAMPLE.COM</code> realm, or phrased even more simply, <code class="literal">B.EXAMPLE.COM</code> now <span class="emphasis"><em>trusts</em></span> <code class="literal">A.EXAMPLE.COM</code>.
</div><div class="para">
This brings us to an important point: cross-realm trust is unidirectional by default. The KDC for the <code class="literal">B.EXAMPLE.COM</code> realm may trust clients from the <code class="literal">A.EXAMPLE.COM</code> to authenticate to services in the <code class="literal">B.EXAMPLE.COM</code> realm, but the fact that it does has no effect on whether or not clients in the <code class="literal">B.EXAMPLE.COM</code> realm are trusted to authenticate to services in the <code class="literal">A.EXAMPLE.COM</code> realm. To establish trust in the other direction, both realms would need to share keys for the <code class="literal">krbtgt/A.EXAMPLE.COM(a)B.EXAMPLE.COM</code> service (take note of the reversed in order of the two realms compared to the example above).
</div><div class="para">
If direct trust relationships were the only method for providing trust between realms, networks which contain multiple realms would be very difficult to set up. Luckily, cross-realm trust is transitive. If clients from <code class="literal">A.EXAMPLE.COM</code> can authenticate to services in <code class="literal">B.EXAMPLE.COM</code>, and clients from <code class="literal">B.EXAMPLE.COM</code> can authenticate to services in <code class="literal">C.EXAMPLE.COM</code>, then clients in <code class="literal">A.EXAMPLE.COM</code> can also authenticate to services in <code class="literal">C.EXAMPLE.COM</code>, <span class="emphasis"><em>even if <code class="literal">C.EXAMPLE.COM</code> doesn't directly trust <code class="literal">A.EXAMPLE.COM</code></em></span>. This means that, on a network with multiple realms which all need to trust each other, making good choices about which trust relationships to set up can greatly reduce the amount of effort required.
</div><div class="para">
Now you face the more conventional problems: the client's system must be configured so that it can properly deduce the realm to which a particular service belongs, and it must be able to determine how to obtain credentials for services in that realm.
</div><div class="para">
First things first: the principal name for a service provided from a specific server system in a given realm typically looks like this:
</div><div class="literallayout"><p>service/server.example.com(a)EXAMPLE.COM<br/>
</p></div><div class="para">
In this example, <span class="emphasis"><em>service</em></span> is typically either the name of the protocol in use (other common values include <span class="emphasis"><em>ldap</em></span>, <span class="emphasis"><em>imap</em></span>, <span class="emphasis"><em>cvs</em></span>, and <span class="emphasis"><em>HTTP</em></span>) or <span class="emphasis"><em>host</em></span>, <span class="emphasis"><em>server.example.com</em></span> is the fully-qualified domain name of the system which runs the service, and <code class="literal">EXAMPLE.COM</code> is the name of the realm.
</div><div class="para">
To deduce the realm to which the service belongs, clients will most often consult DNS or the <code class="literal">domain_realm</code> section of <code class="filename">/etc/krb5.conf</code> to map either a hostname (<span class="emphasis"><em>server.example.com</em></span>) or a DNS domain name (<span class="emphasis"><em>.example.com</em></span>) to the name of a realm (<span class="emphasis"><em>EXAMPLE.COM</em></span>).
</div><div class="para">
Having determined which to which realm a service belongs, a client then has to determine the set of realms which it needs to contact, and in which order it must contact them, to obtain credentials for use in authenticating to the service.
</div><div class="para">
This can be done in one of two ways.
</div><div class="para">
The default method, which requires no explicit configuration, is to give the realms names within a shared hierarchy. For an example, assume realms named <code class="literal">A.EXAMPLE.COM</code>, <code class="literal">B.EXAMPLE.COM</code>, and <code class="literal">EXAMPLE.COM</code>. When a client in the <code class="literal">A.EXAMPLE.COM</code> realm attempts to authenticate to a service in <code class="literal">B.EXAMPLE.COM</code>, it will, by default, first attempt to get credentials for the <code class="literal">EXAMPLE.COM</code> realm, and then to use those credentials to obtain credentials for use in the <code class="literal">B.EXAMPLE.COM</code> realm.
</div><div class="para">
The client in this scenario treats the realm name as one might treat a DNS name. It repeatedly strips off the components of its own realm's name to generate the names of realms which are "above" it in the hierarchy until it reaches a point which is also "above" the service's realm. At that point it begins prepending components of the service's realm name until it reaches the service's realm. Each realm which is involved in the process is another "hop".
</div><div class="para">
For example, using credentials in <code class="literal">A.EXAMPLE.COM</code>, authenticating to a service in <code class="literal">B.EXAMPLE.COM</code><code class="literal">A.EXAMPLE.COM → EXAMPLE.COM → B.EXAMPLE.COM </code>
<div class="itemizedlist"><ul><li><div class="para">
<code class="literal">A.EXAMPLE.COM</code> and <code class="literal">EXAMPLE.COM</code> share a key for <code class="literal">krbtgt/EXAMPLE.COM(a)A.EXAMPLE.COM</code>
</div></li><li><div class="para">
<code class="literal">EXAMPLE.COM</code> and <code class="literal">B.EXAMPLE.COM</code> share a key for <code class="literal">krbtgt/B.EXAMPLE.COM(a)EXAMPLE.COM</code>
</div></li></ul></div>
</div><div class="para">
Another example, using credentials in <code class="literal">SITE1.SALES.EXAMPLE.COM</code>, authenticating to a service in <code class="literal">EVERYWHERE.EXAMPLE.COM</code><code class="literal">SITE1.SALES.EXAMPLE.COM → SALES.EXAMPLE.COM → EXAMPLE.COM → EVERYWHERE.EXAMPLE.COM </code>
<div class="itemizedlist"><ul><li><div class="para">
<code class="literal">SITE1.SALES.EXAMPLE.COM</code> and <code class="literal">SALES.EXAMPLE.COM</code> share a key for <code class="literal">krbtgt/SALES.EXAMPLE.COM(a)SITE1.SALES.EXAMPLE.COM</code>
</div></li><li><div class="para">
<code class="literal">SALES.EXAMPLE.COM</code> and <code class="literal">EXAMPLE.COM</code> share a key for <code class="literal">krbtgt/EXAMPLE.COM(a)SALES.EXAMPLE.COM</code>
</div></li><li><div class="para">
<code class="literal">EXAMPLE.COM</code> and <code class="literal">EVERYWHERE.EXAMPLE.COM</code> share a key for <code class="literal">krbtgt/EVERYWHERE.EXAMPLE.COM(a)EXAMPLE.COM</code>
</div></li></ul></div>
</div><div class="para">
Another example, this time using realm names whose names share no common suffix (<code class="literal">DEVEL.EXAMPLE.COM</code> and <code class="literal">PROD.EXAMPLE.ORG</code><code class="literal"> DEVEL.EXAMPLE.COM → EXAMPLE.COM → COM → ORG → EXAMPLE.ORG → PROD.EXAMPLE.ORG </code>
<div class="itemizedlist"><ul><li><div class="para">
<code class="literal">DEVEL.EXAMPLE.COM</code> and <code class="literal">EXAMPLE.COM</code> share a key for <code class="literal">krbtgt/EXAMPLE.COM(a)DEVEL.EXAMPLE.COM</code>
</div></li><li><div class="para">
<code class="literal">EXAMPLE.COM</code> and <code class="literal">COM</code> share a key for <code class="literal">krbtgt/COM(a)EXAMPLE.COM</code>
</div></li><li><div class="para">
<code class="literal">COM</code> and <code class="literal">ORG</code> share a key for <code class="literal">krbtgt/ORG@COM</code>
</div></li><li><div class="para">
<code class="literal">ORG</code> and <code class="literal">EXAMPLE.ORG</code> share a key for <code class="literal">krbtgt/EXAMPLE.ORG@ORG</code>
</div></li><li><div class="para">
<code class="literal">EXAMPLE.ORG</code> and <code class="literal">PROD.EXAMPLE.ORG</code> share a key for <code class="literal">krbtgt/PROD.EXAMPLE.ORG(a)EXAMPLE.ORG</code>
</div></li></ul></div>
</div><div class="para">
The more complicated, but also more flexible, method involves configuring the <code class="literal">capaths</code> section of <code class="filename">/etc/krb5.conf</code>, so that clients which have credentials for one realm will be able to look up which realm is next in the chain which will eventually lead to the being able to authenticate to servers.
</div><div class="para">
The format of the <code class="literal">capaths</code> section is relatively straightforward: each entry in the section is named after a realm in which a client might exist. Inside of that subsection, the set of intermediate realms from which the client must obtain credentials is listed as values of the key which corresponds to the realm in which a service might reside. If there are no intermediate realms, the value "." is used.
</div><div class="para">
Here's an example:
</div><div class="literallayout"><p> [capaths]<br/>
A.EXAMPLE.COM = {<br/>
B.EXAMPLE.COM = .<br/>
C.EXAMPLE.COM = B.EXAMPLE.COM<br/>
D.EXAMPLE.COM = B.EXAMPLE.COM<br/>
D.EXAMPLE.COM = C.EXAMPLE.COM<br/>
}<br/>
</p></div><div class="para">
In this example, clients in the <code class="literal">A.EXAMPLE.COM</code> realm can obtain cross-realm credentials for <code class="literal">B.EXAMPLE.COM</code> directly from the <code class="literal">A.EXAMPLE.COM</code> KDC.
</div><div class="para">
If those clients wish to contact a service in the<code class="literal">C.EXAMPLE.COM</code> realm, they will first need to obtain necessary credentials from the <code class="literal">B.EXAMPLE.COM</code> realm (this requires that <code class="literal">krbtgt/B.EXAMPLE.COM(a)A.EXAMPLE.COM</code> exist), and then use <code class="literal">those</code> credentials to obtain credentials for use in the <code class="literal">C.EXAMPLE.COM</code> realm (using <code class="literal">krbtgt/C.EXAMPLE.COM(a)B.EXAMPLE.COM</code>).
</div><div class="para">
If those clients wish to contact a service in the <code class="literal">D.EXAMPLE.COM</code> realm, they will first need to obtain necessary credentials from the <code class="literal">B.EXAMPLE.COM</code> realm, and then credentials from the <code class="literal">C.EXAMPLE.COM</code> realm, before finally obtaining credentials for use with the <code class="literal">D.EXAMPLE.COM</code> realm.
</div><div class="note"><h2>Note</h2><div class="para">
Without a capath entry indicating otherwise, Kerberos assumes that cross-realm trust relationships form a hierarchy.
</div><div class="para">
Clients in the <code class="literal">A.EXAMPLE.COM</code> realm can obtain cross-realm credentials from <code class="literal">B.EXAMPLE.COM</code> realm directly. Without the "." indicating this, the client would instead attempt to use a hierarchical path, in this case:
</div><div class="literallayout"><p> A.EXAMPLE.COM → EXAMPLE.COM → B.EXAMPLE.COM<br/>
</p></div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Kerberos-Setting_Up_Secondary_KDCs.html"><strong>Prev</strong>2.6.8. Setting Up Secondary KDCs</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos-Additional_Resources.html"><strong>Next</strong>2.6.10. Additional Resources</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.6.8. Setting Up Secondary KDCs</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Kerberos.html" title="2.6. Kerberos"/><link rel="prev" href="sect-Security_Guide-Kerberos-Domain_to_Realm_Mapping.html" title="2.6.7. Domain-to-Realm Mapping"/><link rel="next" href="sect-Security_Guide-Kerberos-Setting_Up_Cross_Realm_Authentication.html" title="2.6.9. Setting Up Cross Realm Authentication"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Sit
e"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Kerberos-Domain_to_Realm_Mapping.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos-Setting_Up_Cross_Realm_Authentication.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Kerberos-Setting_Up_Secondary_KDCs">2.6.8. Setting Up Secondary KDCs</h3></div></div></div><div class="para">
For a number of reasons, you may choose to run multiple KDCs for a given realm. In this scenario, one KDC (the <span class="emphasis"><em>master KDC</em></span>) keeps a writable copy of the realm database and runs <code class="command">kadmind</code> (it is also your realm's <span class="emphasis"><em>admin server</em></span>), and one or more KDCs (<span class="emphasis"><em>slave KDCs</em></span>) keep read-only copies of the database and run <code class="command">kpropd</code>.
</div><div class="para">
The master-slave propagation procedure entails the master KDC dumping its database to a temporary dump file and then transmitting that file to each of its slaves, which then overwrite their previously-received read-only copies of the database with the contents of the dump file.
</div><div class="para">
To set up a slave KDC, first ensure that the master KDC's <code class="filename">krb5.conf</code> and <code class="filename">kdc.conf</code> files are copied to the slave KDC.
</div><div class="para">
Start <code class="command">kadmin.local</code> from a root shell on the master KDC and use its <code class="command">add_principal</code> command to create a new entry for the master KDC's <span class="emphasis"><em>host</em></span> service, and then use its <code class="command">ktadd</code> command to simultaneously set a random key for the service and store the random key in the master's default keytab file. This key will be used by the <code class="command">kprop</code> command to authenticate to the slave servers. You will only need to do this once, regardless of how many slave servers you install.
</div><div class="literallayout"><p> <code class="computeroutput"><code class="prompt">#</code> <strong class="userinput"><code>kadmin.local -r EXAMPLE.COM</code></strong> Authenticating as principal root/admin(a)EXAMPLE.com with password. <code class="prompt">kadmin:</code> <strong class="userinput"><code>add_principal -randkey host/masterkdc.example.com</code></strong> Principal "host/host/masterkdc.example.com(a)EXAMPLE.COM" created. <code class="prompt">kadmin:</code> <strong class="userinput"><code>ktadd host/masterkdc.example.com</code></strong> Entry for principal host/masterkdc.example.com with kvno 3, encryption type Triple DES cbc mode with \ HMAC/sha1 added to keytab WRFILE:/etc/krb5.keytab. Entry for principal host/masterkdc.example.com with kvno 3, encryption type ArcFour with HMAC/md5 \ added to keytab WRFILE:/etc/krb5.keytab. Entry for principal host/masterkdc.example.com with kvno 3, encryption ty
pe DES with HMAC/sha1 added \ to keytab WRFILE:/etc/krb5.keytab. Entry for principal host/masterkdc.example.com with kvno 3, encryption type DES cbc mode with RSA-MD5 \ added to keytab WRFILE:/etc/krb5.keytab. <code class="prompt">kadmin:</code> <strong class="userinput"><code>quit</code></strong></code><br/>
</p></div><div class="para">
Start <code class="command">kadmin</code> from a root shell on the slave KDC and use its <code class="command">add_principal</code> command to create a new entry for the slave KDC's <span class="emphasis"><em>host</em></span> service, and then use <code class="command">kadmin</code>'s <code class="command">ktadd</code> command to simultaneously set a random key for the service and store the random key in the slave's default keytab file. This key is used by the <code class="command">kpropd</code> service when authenticating clients.
</div><div class="literallayout"><p> <code class="computeroutput"><code class="prompt">#</code> <strong class="userinput"><code>kadmin -p jimbo/admin(a)EXAMPLE.com -r example.COM</code></strong> Authenticating as principal jimbo/admin(a)EXAMPLE.com with password. <code class="prompt">Password for jimbo/admin@EXAMPLE.COM: </code><code class="prompt">kadmin:</code> <strong class="userinput"><code>add_principal -randkey host/slavekdc.example.com</code></strong> Principal "host/slavekdc.example.com(a)EXAMPLE.COM" created. <code class="prompt">kadmin:</code> <strong class="userinput"><code>ktadd host/slavekdc.example.com(a)EXAMPLE.COM</code></strong> Entry for principal host/slavekdc.example.com with kvno 3, encryption type Triple DES cbc mode with \ HMAC/sha1 added to keytab WRFILE:/etc/krb5.keytab. Entry for principal host/slavekdc.example.com with kvno 3, encryption type ArcFour with HMAC/md5 added \ to keytab WRFILE:/etc/
krb5.keytab. Entry for principal host/slavekdc.example.com with kvno 3, encryption type DES with HMAC/sha1 added \ to keytab WRFILE:/etc/krb5.keytab. Entry for principal host/slavekdc.example.com with kvno 3, encryption type DES cbc mode with RSA-MD5 added \ to keytab WRFILE:/etc/krb5.keytab. <code class="prompt">kadmin:</code> <strong class="userinput"><code>quit</code></strong></code><br/>
</p></div><div class="para">
With its service key, the slave KDC could authenticate any client which would connect to it. Obviously, not all of them should be allowed to provide the slave's <code class="command">kprop</code> service with a new realm database. To restrict access, the <code class="command">kprop</code> service on the slave KDC will only accept updates from clients whose principal names are listed in <code class="filename">/var/kerberos/krb5kdc/kpropd.acl</code>. Add the master KDC's host service's name to that file.
</div><div class="literallayout"><p> <code class="computeroutput"><code class="prompt">#</code> <strong class="userinput"><code>echo host/masterkdc.example.com(a)EXAMPLE.com > /var/kerberos/krb5kdc/kpropd.acl</code></strong></code><br/>
</p></div><div class="para">
Once the slave KDC has obtained a copy of the database, it will also need the master key which was used to encrypt it. If your KDC database's master key is stored in a <span class="emphasis"><em>stash</em></span> file on the master KDC (typically named <code class="filename">/var/kerberos/krb5kdc/.k5.REALM</code>, either copy it to the slave KDC using any available secure method, or create a dummy database and identical stash file on the slave KDC by running <code class="command">kdb5_util create -s</code> (the dummy database will be overwritten by the first successful database propagation) and supplying the same password.
</div><div class="para">
Ensure that the slave KDC's firewall allows the master KDC to contact it using TCP on port 754 (<span class="emphasis"><em>krb5_prop</em></span>), and start the <code class="command">kprop</code> service. Then, double-check that the <code class="command">kadmin</code> service is <span class="emphasis"><em>disabled</em></span>.
</div><div class="para">
Now perform a manual database propagation test by dumping the realm database, on the master KDC, to the default data file which the <code class="command">kprop</code> command will read (<code class="filename">/var/kerberos/krb5kdc/slave_datatrans</code>), and then use the <code class="command">kprop</code> command to transmit its contents to the slave KDC.
</div><div class="literallayout"><p> <code class="computeroutput"><code class="prompt">#</code> <strong class="userinput"><code>/usr/kerberos/sbin/kdb5_util dump /var/kerberos/krb5kdc/slave_datatrans</code></strong><code class="prompt">#</code> <strong class="userinput"><code>kprop slavekdc.example.com</code></strong></code><br/>
</p></div><div class="para">
Using <code class="command">kinit</code>, verify that a client system whose <code class="filename">krb5.conf</code> lists only the slave KDC in its list of KDCs for your realm is now correctly able to obtain initial credentials from the slave KDC.
</div><div class="para">
That done, simply create a script which dumps the realm database and runs the <code class="command">kprop</code> command to transmit the database to each slave KDC in turn, and configure the <code class="command">cron</code> service to run the script periodically.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Kerberos-Domain_to_Realm_Mapping.html"><strong>Prev</strong>2.6.7. Domain-to-Realm Mapping</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos-Setting_Up_Cross_Realm_Authentication.html"><strong>Next</strong>2.6.9. Setting Up Cross Realm Authentication</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.6. Kerberos</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="chap-Security_Guide-Securing_Your_Network.html" title="Chapter 2. Securing Your Network"/><link rel="prev" href="sect-Security_Guide-Additional_Resources-Related_Books.html" title="2.5.5.3. Related Books"/><link rel="next" href="sect-Security_Guide-Kerberos-Kerberos_Terminology.html" title="2.6.2. Kerberos Terminology"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="doc
nav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Additional_Resources-Related_Books.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos-Kerberos_Terminology.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-Kerberos">2.6. Kerberos</h2></div></div></div><a id="d0e9180" class="indexterm"/><div class="para">
System security and integrity within a network can be unwieldy. It can occupy the time of several administrators just to keep track of what services are being run on a network and the manner in which these services are used.
</div><div class="para">
Further, authenticating users to network services can prove dangerous when the method used by the protocol is inherently insecure, as evidenced by the transfer of unencrypted passwords over a network using the traditional FTP and Telnet protocols.
</div><div class="para">
Kerberos is a way to eliminate the need for protocols that allow unsafe methods of authentication, thereby enhancing overall network security.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Kerberos-What_is_Kerberos">2.6.1. What is Kerberos?</h3></div></div></div><div class="para">
Kerberos is a network authentication protocol created by MIT, and uses symmetric-key cryptography<sup>[<a id="d0e9196" href="#ftn.d0e9196" class="footnote">8</a>]</sup> to authenticate users to network services, which means passwords are never actually sent over the network.
</div><div class="para">
Consequently, when users authenticate to network services using Kerberos, unauthorized users attempting to gather passwords by monitoring network traffic are effectively thwarted.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-What_is_Kerberos-Advantages_of_Kerberos">2.6.1.1. Advantages of Kerberos</h4></div></div></div><a id="d0e9205" class="indexterm"/><div class="para">
Most conventional network services use password-based authentication schemes. Such schemes require a user to authenticate to a given network server by supplying their username and password. Unfortunately, the transmission of authentication information for many services is unencrypted. For such a scheme to be secure, the network has to be inaccessible to outsiders, and all computers and users on the network must be trusted and trustworthy.
</div><div class="para">
Even if this is the case, a network that is connected to the Internet can no longer be assumed to be secure. Any attacker who gains access to the network can use a simple packet analyzer, also known as a packet sniffer, to intercept usernames and passwords, compromising user accounts and the integrity of the entire security infrastructure.
</div><div class="para">
The primary design goal of Kerberos is to eliminate the transmission of unencrypted passwords across the network. If used properly, Kerberos effectively eliminates the threat that packet sniffers would otherwise pose on a network.
</div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-What_is_Kerberos-Disadvantages_of_Kerberos">2.6.1.2. Disadvantages of Kerberos</h4></div></div></div><a id="d0e9219" class="indexterm"/><div class="para">
Although Kerberos removes a common and severe security threat, it may be difficult to implement for a variety of reasons:
</div><div class="itemizedlist"><ul><li><div class="para">
Migrating user passwords from a standard UNIX password database, such as <code class="filename">/etc/passwd</code> or <code class="filename">/etc/shadow</code>, to a Kerberos password database can be tedious, as there is no automated mechanism to perform this task. Refer to Question 2.23 in the online Kerberos FAQ:
</div><div class="para">
<a href="http://www.nrl.navy.mil/CCS/people/kenh/kerberos-faq.html#pwconvert"> http://www.nrl.navy.mil/CCS/people/kenh/kerberos-faq.html</a>
</div></li><li><div class="para">
Kerberos has only partial compatibility with the Pluggable Authentication Modules (PAM) system used by most Fedora servers. Refer to <a class="xref" href="sect-Security_Guide-Kerberos-Kerberos_and_PAM.html" title="2.6.4. Kerberos and PAM">Section 2.6.4, “Kerberos and PAM”</a> for more information about this issue.
</div></li><li><div class="para">
Kerberos assumes that each user is trusted but is using an untrusted host on an untrusted network. Its primary goal is to prevent unencrypted passwords from being transmitted across that network. However, if anyone other than the proper user has access to the one host that issues tickets used for authentication — called the <em class="firstterm">key distribution center</em> (<em class="firstterm">KDC</em>) — the entire Kerberos authentication system is at risk.
</div></li><li><div class="para">
For an application to use Kerberos, its source must be modified to make the appropriate calls into the Kerberos libraries. Applications modified in this way are considered to be <em class="firstterm">Kerberos-aware</em>, or <em class="firstterm">kerberized</em>. For some applications, this can be quite problematic due to the size of the application or its design. For other incompatible applications, changes must be made to the way in which the server and client communicate. Again, this may require extensive programming. Closed-source applications that do not have Kerberos support by default are often the most problematic.
</div></li><li><div class="para">
Kerberos is an all-or-nothing solution. If Kerberos is used on the network, any unencrypted passwords transferred to a non-Kerberos aware service is at risk. Thus, the network gains no benefit from the use of Kerberos. To secure a network with Kerberos, one must either use Kerberos-aware versions of <span class="emphasis"><em>all</em></span> client/server applications that transmit passwords unencrypted, or not use <span class="emphasis"><em>any</em></span> such client/server applications at all.
</div></li></ul></div></div></div><div class="footnotes"><br/><hr/><div class="footnote"><p><sup>[<a id="ftn.d0e9196" href="#d0e9196" class="para">8</a>] </sup>
A system where both the client and the server share a common key that is used to encrypt and decrypt network communication.
</p></div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Additional_Resources-Related_Books.html"><strong>Prev</strong>2.5.5.3. Related Books</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Kerberos-Kerberos_Terminology.html"><strong>Next</strong>2.6.2. Kerberos Terminology</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>3.7.5. Links of Interest</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-LUKS_Disk_Encryption.html" title="3.7. LUKS Disk Encryption"/><link rel="prev" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-What_you_have_just_accomplished.html" title="3.7.4. What you have just accomplished."/><link rel="next" href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives.html" title="3.8. 7-Zip Encrypted Archives"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Con
tent/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-What_you_have_just_accomplished.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-LUKS_Disk_Encryption-Links_of_Interest">3.7.5. Links of Interest</h3></div></div></div><div class="para">
For additional information on LUKS or encrypting hard drives under Fedora please visit one of the following links:
</div><div class="itemizedlist"><ul><li><div class="para">
<a href="http://luks.endorphin.org/">LUKS - Linux Unified Key Setup</a>
</div></li><li><div class="para">
<a href="https://bugzilla.redhat.com/attachment.cgi?id=161912">HOWTO: Creating an encrypted Physical Volume (PV) using a second hard drive, pvmove, and a Fedora LiveCD</a>
</div></li></ul></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-What_you_have_just_accomplished.html"><strong>Prev</strong>3.7.4. What you have just accomplished.</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Encryption-7_Zip_Encrypted_Archives.html"><strong>Next</strong>3.8. 7-Zip Encrypted Archives</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>3.7.3. Step-by-Step Instructions</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-LUKS_Disk_Encryption.html" title="3.7. LUKS Disk Encryption"/><link rel="prev" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories.html" title="3.7.2. Manually Encrypting Directories"/><link rel="next" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-What_you_have_just_accomplished.html" title="3.7.4. What you have just accomplished."/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedor
aproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-What_you_have_just_accomplished.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-Step_by_Step_Instructions">3.7.3. Step-by-Step Instructions</h3></div></div></div><div class="orderedlist"><ol><li><div class="para">
enter runlevel 1: <code class="code">telinit 1</code>
</div></li><li><div class="para">
unmount your existing /home: <code class="code"> umount /home</code>
</div></li><li><div class="para">
if it fails use <code class="code">fuser</code> to find and kill processes hogging /home: <code class="code">fuser -mvk /home</code>
</div></li><li><div class="para">
verify /home is not mounted any longer: <code class="code">cat /proc/mounts | grep home</code>
</div></li><li><div class="para">
Fill your partition with random data: <code class="code">dd if=/dev/urandom of=/dev/VG00/LV_home</code> This process takes many hours to complete.
</div><div class="important"><h2>Important</h2><div class="para">
The process, however, is imperative in order to have good protection against break-in attempts. Just let it run overnight.
</div></div></li><li><div class="para">
initialize your partition: <code class="code">cryptsetup --verbose --verify-passphrase luksFormat /dev/VG00/LV_home</code>
</div></li><li><div class="para">
open the newly encrypted device: <code class="code">cryptsetup luksOpen /dev/VG00/LV_home home</code>
</div></li><li><div class="para">
check it's there: <code class="code">ls -l /dev/mapper | grep home</code>
</div></li><li><div class="para">
create a filesystem: <code class="code">mkfs.ext3 /dev/mapper/home</code>
</div></li><li><div class="para">
mount it: <code class="code">mount /dev/mapper/home /home</code>
</div></li><li><div class="para">
check it's visible: <code class="code">df -h | grep home</code>
</div></li><li><div class="para">
add the following to /etc/crypttab: <code class="code">home /dev/VG00/LV_home none</code>
</div></li><li><div class="para">
edit your /etc/fstab, removing the old entry for /home and adding <code class="code">/dev/mapper/home /home ext3 defaults 1 2</code>
</div></li><li><div class="para">
verify your fstab entry: <code class="code">mount /home</code>
</div></li><li><div class="para">
restore default SELinux security contexts: <code class="code">/sbin/restorecon -v -R /home</code>
</div></li><li><div class="para">
reboot: <code class="code">shutdown -r now</code>
</div></li><li><div class="para">
The entry in /etc/crypttab makes your computer ask your <code class="code">luks</code> passphrase on boot
</div></li><li><div class="para">
Login as root and restore your backup
</div></li></ol></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories.html"><strong>Prev</strong>3.7.2. Manually Encrypting Directories</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-What_you_have_just_accomplished.html"><strong>Next</strong>3.7.4. What you have just accomplished.</a></li></ul></body></html>
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tent/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-Step_by_Step_Instructions.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-LUKS_Disk_Encryption-Links_of_Interest.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-What_you_have_just_accomplished">3.7.4. What you have just accomplished.</h3></div></div></div><div class="para">
Congratulations, you now have an encrypted partition for all of your data to safely rest while the computer is off.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-Step_by_Step_Instructions.html"><strong>Prev</strong>3.7.3. Step-by-Step Instructions</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-LUKS_Disk_Encryption-Links_of_Interest.html"><strong>Next</strong>3.7.5. Links of Interest</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>3.7.2. Manually Encrypting Directories</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-LUKS_Disk_Encryption.html" title="3.7. LUKS Disk Encryption"/><link rel="prev" href="sect-Security_Guide-LUKS_Disk_Encryption.html" title="3.7. LUKS Disk Encryption"/><link rel="next" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-Step_by_Step_Instructions.html" title="3.7.3. Step-by-Step Instructions"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_
right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-LUKS_Disk_Encryption.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-Step_by_Step_Instructions.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories">3.7.2. Manually Encrypting Directories</h3></div></div></div><div class="warning"><h2>Warning</h2><div class="para">
Following this procedure will remove all data on the partition that you are encrypting. You WILL lose all your information! Make sure you backup your data to an external source before beginning this procedure!
</div></div><div class="para">
If you are running a version of Fedora prior to Fedora 9 and want to encrypt a partition, or you want to encrypt a partition after the installation of the current version of Fedora, the following directions are for you. The below example demonstrates encrypting your /home partition but any partition can be used.
</div><div class="para">
The following procedure will wipe all your existing data, so be sure to have a tested backup before you start. This also requires you to have a separate partition for /home (in my case that is /dev/VG00/LV_home). All the following must be done as root. Any of these steps failing means you must not continue until the step succeeded.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-LUKS_Disk_Encryption.html"><strong>Prev</strong>3.7. LUKS Disk Encryption</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories-Step_by_Step_Instructions.html"><strong>Next</strong>3.7.3. Step-by-Step Instructions</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>3.7. LUKS Disk Encryption</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="chap-Security_Guide-Encryption.html" title="Chapter 3. Encryption"/><link rel="prev" href="Security_Guide-Encryption-Data_in_Motion-Secure_Shell.html" title="3.6. Secure Shell"/><link rel="next" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories.html" title="3.7.2. Manually Encrypting Directories"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a>
</p><ul class="docnav"><li class="previous"><a accesskey="p" href="Security_Guide-Encryption-Data_in_Motion-Secure_Shell.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title" id="sect-Security_Guide-LUKS_Disk_Encryption">3.7. LUKS Disk Encryption</h2></div></div></div><div class="para">
Linux Unified Key Setup-on-disk-format (or LUKS) allows you to encrypt partitions on your Linux computer. This is particularly important when it comes to mobile computers and removable media. LUKS allows multiple user keys to decrypt a master key which is used for the bulk encryption of the partition.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-LUKS_Disk_Encryption-LUKS_Implementation_in_Fedora">3.7.1. LUKS Implementation in Fedora</h3></div></div></div><div class="para">
Fedora 9, and later, utilizes LUKS to perform file system encryption. By default, the option to encrypt the file system is unchecked during the installation. If you select the option to encrypt you hard drive, you will be prompted for a passphrase that will be asked every time you boot the computer. This passphrase "unlocks" the bulk encryption key that is used to decrypt your partition. If you choose to modify the default partition table you can choose which partitions you want to encrypt. This is set in the partition table settings
</div><div class="para">
Fedora 9's default implementation of LUKS is AES 128 with a SHA256 hashing. Ciphers that are available are:
</div><div class="itemizedlist"><ul><li><div class="para">
AES - Advanced Encryption Standard - <a href="http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf">FIPS PUB 197</a>
</div></li><li><div class="para">
Twofish (A 128-bit Block Cipher)
</div></li><li><div class="para">
Serpent
</div></li><li><div class="para">
cast5 - RFC 2144
</div></li><li><div class="para">
cast6 - RFC 2612
</div></li></ul></div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="Security_Guide-Encryption-Data_in_Motion-Secure_Shell.html"><strong>Prev</strong>3.6. Secure Shell</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-LUKS_Disk_Encryption-Manually_Encrypting_Directories.html"><strong>Next</strong>3.7.2. Manually Encrypting Directories</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.5.2.2.2. Access Control</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-TCP_Wrappers_Configuration_Files-Option_Fields.html" title="2.5.2.2. Option Fields"/><link rel="prev" href="sect-Security_Guide-TCP_Wrappers_Configuration_Files-Option_Fields.html" title="2.5.2.2. Option Fields"/><link rel="next" href="sect-Security_Guide-Option_Fields-Shell_Commands.html" title="2.5.2.2.3. Shell Commands"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Document
ation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-TCP_Wrappers_Configuration_Files-Option_Fields.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Option_Fields-Shell_Commands.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Option_Fields-Access_Control">2.5.2.2.2. Access Control</h5></div></div></div><a id="d0e7930" class="indexterm"/><div class="para">
Option fields also allow administrators to explicitly allow or deny hosts in a single rule by adding the <code class="option">allow</code> or <code class="option">deny</code> directive as the final option.
</div><div class="para">
For example, the following two rules allow SSH connections from <code class="systemitem">client-1.example.com</code>, but deny connections from <code class="systemitem">client-2.example.com</code>:
</div><pre class="screen">sshd : client-1.example.com : allow
sshd : client-2.example.com : deny
</pre><div class="para">
By allowing access control on a per-rule basis, the option field allows administrators to consolidate all access rules into a single file: either <code class="filename">hosts.allow</code> or <code class="filename">hosts.deny</code>. Some administrators consider this an easier way of organizing access rules.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-TCP_Wrappers_Configuration_Files-Option_Fields.html"><strong>Prev</strong>2.5.2.2. Option Fields</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Option_Fields-Shell_Commands.html"><strong>Next</strong>2.5.2.2.3. Shell Commands</a></li></ul></body></html>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.5.2.2.4. Expansions</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-TCP_Wrappers_Configuration_Files-Option_Fields.html" title="2.5.2.2. Option Fields"/><link rel="prev" href="sect-Security_Guide-Option_Fields-Shell_Commands.html" title="2.5.2.2.3. Shell Commands"/><link rel="next" href="sect-Security_Guide-TCP_Wrappers_and_xinetd-xinetd.html" title="2.5.3. xinetd"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul clas
s="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Option_Fields-Shell_Commands.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-TCP_Wrappers_and_xinetd-xinetd.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Option_Fields-Expansions">2.5.2.2.4. Expansions</h5></div></div></div><a id="d0e8040" class="indexterm"/><div class="para">
Expansions, when used in conjunction with the <code class="command">spawn</code> and <code class="command">twist</code> directives, provide information about the client, server, and processes involved.
</div><div class="para">
The following is a list of supported expansions:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="option">%a</code> — Returns the client's IP address.
</div></li><li><div class="para">
<code class="option">%A</code> — Returns the server's IP address.
</div></li><li><div class="para">
<code class="option">%c</code> — Returns a variety of client information, such as the username and hostname, or the username and IP address.
</div></li><li><div class="para">
<code class="option">%d</code> — Returns the daemon process name.
</div></li><li><div class="para">
<code class="option">%h</code> — Returns the client's hostname (or IP address, if the hostname is unavailable).
</div></li><li><div class="para">
<code class="option">%H</code> — Returns the server's hostname (or IP address, if the hostname is unavailable).
</div></li><li><div class="para">
<code class="option">%n</code> — Returns the client's hostname. If unavailable, <code class="computeroutput">unknown</code> is printed. If the client's hostname and host address do not match, <code class="computeroutput">paranoid</code> is printed.
</div></li><li><div class="para">
<code class="option">%N</code> — Returns the server's hostname. If unavailable, <code class="computeroutput">unknown</code> is printed. If the server's hostname and host address do not match, <code class="computeroutput">paranoid</code> is printed.
</div></li><li><div class="para">
<code class="option">%p</code> — Returns the daemon's process ID.
</div></li><li><div class="para">
<code class="option">%s</code> —Returns various types of server information, such as the daemon process and the host or IP address of the server.
</div></li><li><div class="para">
<code class="option">%u</code> — Returns the client's username. If unavailable, <code class="computeroutput">unknown</code> is printed.
</div></li></ul></div><div class="para">
The following sample rule uses an expansion in conjunction with the <code class="command">spawn</code> command to identify the client host in a customized log file.
</div><div class="para">
When connections to the SSH daemon (<code class="systemitem">sshd</code>) are attempted from a host in the <code class="systemitem">example.com</code> domain, execute the <code class="command">echo</code> command to log the attempt, including the client hostname (by using the <code class="option">%h</code> expansion), to a special file:
</div><pre class="screen">sshd : .example.com \
: spawn /bin/echo `/bin/date` access denied to %h>>/var/log/sshd.log \
: deny
</pre><div class="para">
Similarly, expansions can be used to personalize messages back to the client. In the following example, clients attempting to access FTP services from the <code class="systemitem">example.com</code> domain are informed that they have been banned from the server:
</div><pre class="screen">vsftpd : .example.com \
: twist /bin/echo "421 %h has been banned from this server!"
</pre><div class="para">
For a full explanation of available expansions, as well as additional access control options, refer to section 5 of the man pages for <code class="filename">hosts_access</code> (<code class="command">man 5 hosts_access</code>) and the man page for <code class="filename">hosts_options</code>.
</div><div class="para">
Refer to <a class="xref" href="sect-Security_Guide-TCP_Wrappers_and_xinetd-Additional_Resources.html" title="2.5.5. Additional Resources">Section 2.5.5, “Additional Resources”</a> for more information about TCP Wrappers.
</div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Option_Fields-Shell_Commands.html"><strong>Prev</strong>2.5.2.2.3. Shell Commands</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-TCP_Wrappers_and_xinetd-xinetd.html"><strong>Next</strong>2.5.3. xinetd</a></li></ul></body></html>
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l class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Option_Fields-Access_Control.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Option_Fields-Expansions.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h5 class="title" id="sect-Security_Guide-Option_Fields-Shell_Commands">2.5.2.2.3. Shell Commands</h5></div></div></div><a id="d0e7966" class="indexterm"/><a id="d0e7973" class="indexterm"/><a id="d0e7982" class="indexterm"/><div class="para">
Option fields allow access rules to launch shell commands through the following two directives:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="command">spawn</code> — Launches a shell command as a child process. This directive can perform tasks like using <code class="command">/usr/sbin/safe_finger</code> to get more information about the requesting client or create special log files using the <code class="command">echo</code> command.
</div><div class="para">
In the following example, clients attempting to access Telnet services from the <code class="systemitem">example.com</code> domain are quietly logged to a special file:
</div><pre class="screen">in.telnetd : .example.com \
: spawn /bin/echo `/bin/date` from %h>>/var/log/telnet.log \
: allow
</pre></li><li><div class="para">
<code class="command">twist</code> — Replaces the requested service with the specified command. This directive is often used to set up traps for intruders (also called "honey pots"). It can also be used to send messages to connecting clients. The <code class="command">twist</code> directive must occur at the end of the rule line.
</div><div class="para">
In the following example, clients attempting to access FTP services from the <code class="systemitem">example.com</code> domain are sent a message using the <code class="command">echo</code> command:
</div><pre class="screen">vsftpd : .example.com \
: twist /bin/echo "421 This domain has been black-listed. Access denied!"
</pre></li></ul></div><div class="para">
For more information about shell command options, refer to the <code class="filename">hosts_options</code> man page.
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.4.3.2. Control Flag</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_Configuration_File_Format.html" title="2.4.3. PAM Configuration File Format"/><link rel="prev" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_Configuration_File_Format.html" title="2.4.3. PAM Configuration File Format"/><link rel="next" href="sect-Security_Guide-PAM_Configuration_File_Format-Module_Name.html" title="2.4.3.3. Module Name"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedorapro
ject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_Configuration_File_Format.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-PAM_Configuration_File_Format-Module_Name.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-PAM_Configuration_File_Format-Control_Flag">2.4.3.2. Control Flag</h4></div></div></div><a id="d0e6266" class="indexterm"/><div class="para">
All PAM modules generate a success or failure result when called. Control flags tell PAM what do with the result. Modules can be stacked in a particular order, and the control flags determine how important the success or failure of a particular module is to the overall goal of authenticating the user to the service.
</div><div class="para">
There are four predefined control flags:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="command">required</code> — The module result must be successful for authentication to continue. If the test fails at this point, the user is not notified until the results of all module tests that reference that interface are complete.
</div></li><li><div class="para">
<code class="command">requisite</code> — The module result must be successful for authentication to continue. However, if a test fails at this point, the user is notified immediately with a message reflecting the first failed <code class="command">required</code> <span class="emphasis"><em>or</em></span> <code class="command">requisite</code> module test.
</div></li><li><div class="para">
<code class="command">sufficient</code> — The module result is ignored if it fails. However, if the result of a module flagged <code class="command">sufficient</code> is successful <span class="emphasis"><em>and</em></span> no previous modules flagged <code class="command">required</code> have failed, then no other results are required and the user is authenticated to the service.
</div></li><li><div class="para">
<code class="command">optional</code> — The module result is ignored. A module flagged as <code class="command">optional</code> only becomes necessary for successful authentication when no other modules reference the interface.
</div></li></ul></div><div class="important"><h2>Important</h2><div class="para">
The order in which <code class="command">required</code> modules are called is not critical. Only the <code class="command">sufficient</code> and <code class="command">requisite</code> control flags cause order to become important.
</div></div><div class="para">
A newer control flag syntax that allows for more precise control is now available for PAM.
</div><div class="para">
The <code class="command">pam.d</code> man page, and the PAM documentation, located in the <code class="filename">/usr/share/doc/pam-<em class="replaceable"><code><version-number></code></em>/</code> directory, where <em class="replaceable"><code><version-number></code></em> is the version number for PAM on your system, describe this newer syntax in detail.
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.4.3.4. Module Arguments</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_Configuration_File_Format.html" title="2.4.3. PAM Configuration File Format"/><link rel="prev" href="sect-Security_Guide-PAM_Configuration_File_Format-Module_Name.html" title="2.4.3.3. Module Name"/><link rel="next" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Sample_PAM_Configuration_Files.html" title="2.4.4. Sample PAM Configuration Files"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fed
oraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-PAM_Configuration_File_Format-Module_Name.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Sample_PAM_Configuration_Files.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-PAM_Configuration_File_Format-Module_Arguments">2.4.3.4. Module Arguments</h4></div></div></div><a id="d0e6375" class="indexterm"/><div class="para">
PAM uses <em class="firstterm">arguments</em> to pass information to a pluggable module during authentication for some modules.
</div><div class="para">
For example, the <code class="filename">pam_userdb.so</code> module uses information stored in a Berkeley DB file to authenticate the user. Berkeley DB is an open source database system embedded in many applications. The module takes a <code class="filename">db</code> argument so that Berkeley DB knows which database to use for the requested service.
</div><div class="para">
The following is a typical <code class="filename">pam_userdb.so</code> line in a PAM configuration. The <em class="replaceable"><code><path-to-file></code></em> is the full path to the Berkeley DB database file:
</div><pre class="screen">auth required pam_userdb.so db=<em class="replaceable"><code><path-to-file></code></em>
</pre><div class="para">
Invalid arguments are <span class="emphasis"><em>generally</em></span> ignored and do not otherwise affect the success or failure of the PAM module. Some modules, however, may fail on invalid arguments. Most modules report errors to the <code class="filename">/var/log/secure</code> file.
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.4.3.3. Module Name</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_Configuration_File_Format.html" title="2.4.3. PAM Configuration File Format"/><link rel="prev" href="sect-Security_Guide-PAM_Configuration_File_Format-Control_Flag.html" title="2.4.3.2. Control Flag"/><link rel="next" href="sect-Security_Guide-PAM_Configuration_File_Format-Module_Arguments.html" title="2.4.3.4. Module Arguments"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Con
tent/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-PAM_Configuration_File_Format-Control_Flag.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-PAM_Configuration_File_Format-Module_Arguments.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-PAM_Configuration_File_Format-Module_Name">2.4.3.3. Module Name</h4></div></div></div><a id="d0e6354" class="indexterm"/><div class="para">
The module name provides PAM with the name of the pluggable module containing the specified module interface. In older versions of Fedora, the full path to the module was provided in the PAM configuration file. However, since the advent of <em class="firstterm">multilib</em> systems, which store 64-bit PAM modules in the <code class="filename">/lib64/security/</code> directory, the directory name is omitted because the application is linked to the appropriate version of <code class="filename">libpam</code>, which can locate the correct version of the module.
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.4.6.2. Common pam_timestamp Directives</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Administrative_Credential_Caching.html" title="2.4.6. PAM and Administrative Credential Caching"/><link rel="prev" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Administrative_Credential_Caching.html" title="2.4.6. PAM and Administrative Credential Caching"/><link rel="next" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Device_Ownership.html" title="2.4.7. PAM and Device Ownership"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_C
ontent/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Administrative_Credential_Caching.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Device_Ownership.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-PAM_and_Administrative_Credential_Caching-Common_pam_timestamp_Directives">2.4.6.2. Common pam_timestamp Directives</h4></div></div></div><a id="d0e6774" class="indexterm"/><div class="para">
The <code class="filename">pam_timestamp.so</code> module accepts several directives. The following are the two most commonly used options:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="command">timestamp_timeout</code> — Specifies the period (in seconds) for which the timestamp file is valid. The default value is 300 (five minutes).
</div></li><li><div class="para">
<code class="command">timestampdir</code> — Specifies the directory in which the timestamp file is stored. The default value is <code class="command">/var/run/sudo/</code>.
</div></li></ul></div><div class="para">
Refer to <a class="xref" href="sect-Security_Guide-Firewalls-Additional_Resources.html#sect-Security_Guide-Additional_Resources-Installed_Firewall_Documentation" title="2.8.9.1. Installed Firewall Documentation">Section 2.8.9.1, “Installed Firewall Documentation”</a> for more information about controlling the <code class="filename">pam_timestamp.so</code> module.
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.4.7.2. Application Access</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Device_Ownership.html" title="2.4.7. PAM and Device Ownership"/><link rel="prev" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Device_Ownership.html" title="2.4.7. PAM and Device Ownership"/><link rel="next" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Additional_Resources.html" title="2.4.8. Additional Resources"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.
fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Device_Ownership.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Additional_Resources.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-PAM_and_Device_Ownership-Application_Access">2.4.7.2. Application Access</h4></div></div></div><div class="para">
The console user also has access to certain programs configured for use in the <code class="filename">/etc/security/console.apps/</code> directory.
</div><div class="para">
This directory contains configuration files which enable the console user to run certain applications in <code class="filename">/sbin</code> and <code class="filename">/usr/sbin</code>.
</div><div class="para">
These configuration files have the same name as the applications that they set up.
</div><div class="para">
One notable group of applications that the console user has access to are three programs that shut down or reboot the system:
</div><div class="itemizedlist"><ul><li><div class="para">
<code class="command">/sbin/halt</code>
</div></li><li><div class="para">
<code class="command">/sbin/reboot</code>
</div></li><li><div class="para">
<code class="command">/sbin/poweroff</code>
</div></li></ul></div><div class="para">
Because these are PAM-aware applications, they call the <code class="filename">pam_console.so</code> module as a requirement for use.
</div><div class="para">
Refer to <a class="xref" href="sect-Security_Guide-Firewalls-Additional_Resources.html#sect-Security_Guide-Additional_Resources-Installed_Firewall_Documentation" title="2.8.9.1. Installed Firewall Documentation">Section 2.8.9.1, “Installed Firewall Documentation”</a> for more information.
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>2.4.8. Additional Resources</title><link rel="stylesheet" href="./Common_Content/css/default.css" type="text/css"/><meta name="generator" content="publican"/><meta name="package" content="fedora-Linux_Security_Guide-10-en-US-1.0-3"/><link rel="home" href="index.html" title="Linux Security Guide"/><link rel="up" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM.html" title="2.4. Pluggable Authentication Modules (PAM)"/><link rel="prev" href="sect-Security_Guide-PAM_and_Device_Ownership-Application_Access.html" title="2.4.7.2. Application Access"/><link rel="next" href="sect-Security_Guide-Additional_Resources-Useful_PAM_Websites.html" title="2.4.8.2. Useful PAM Websites"/></head><body><p id="title"><a class="left" href="http://www.fedoraproject.org"><img src="Common_Content/images/image_left.png" alt="Product Site"/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/
image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-PAM_and_Device_Ownership-Application_Access.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Additional_Resources-Useful_PAM_Websites.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Additional_Resources">2.4.8. Additional Resources</h3></div></div></div><a id="d0e7004" class="indexterm"/><div class="para">
The following resources further explain methods to use and configure PAM. In addition to these resources, read the PAM configuration files on the system to better understand how they are structured.
</div><div class="section" lang="en-US"><div class="titlepage"><div><div><h4 class="title" id="sect-Security_Guide-Additional_Resources-Installed_PAM_Documentation">2.4.8.1. Installed PAM Documentation</h4></div></div></div><a id="d0e7014" class="indexterm"/><div class="itemizedlist"><ul><li><div class="para">
PAM-related man pages — Several man pages exist for the various applications and configuration files involved with PAM. The following is a list of some of the more important man pages.
</div><div class="variablelist"><dl><dt><span class="term">Configuration Files</span></dt><dd><div class="itemizedlist"><ul><li><div class="para">
<code class="command">pam</code> — Good introductory information on PAM, including the structure and purpose of the PAM configuration files.
</div><div class="para">
Note that this man page discusses both <code class="filename">/etc/pam.conf</code> and individual configuration files in the <code class="filename">/etc/pam.d/</code> directory. By default, Fedora uses the individual configuration files in the <code class="filename">/etc/pam.d/</code> directory, ignoring <code class="filename">/etc/pam.conf</code> even if it exists.
</div></li><li><div class="para">
<code class="command">pam_console</code> — Describes the purpose of the <code class="filename">pam_console.so</code> module. It also describes the appropriate syntax for an entry within a PAM configuration file.
</div></li><li><div class="para">
<code class="command">console.apps</code> — Describes the format and options available in the <code class="filename">/etc/security/console.apps</code> configuration file, which defines which applications are accessible by the console user assigned by PAM.
</div></li><li><div class="para">
<code class="command">console.perms</code> — Describes the format and options available in the <code class="filename">/etc/security/console.perms</code> configuration file, which specifies the console user permissions assigned by PAM.
</div></li><li><div class="para">
<code class="command">pam_timestamp</code> — Describes the <code class="filename">pam_timestamp.so</code> module.
</div></li></ul></div></dd></dl></div></li><li><div class="para">
<code class="filename">/usr/share/doc/pam-<em class="replaceable"><code><version-number></code></em></code> — Contains a <em class="citetitle">System Administrators' Guide</em>, a <em class="citetitle">Module Writers' Manual</em>, and the <em class="citetitle">Application Developers' Manual</em>, as well as a copy of the PAM standard, DCE-RFC 86.0, where <em class="replaceable"><code><version-number></code></em> is the version number of PAM.
</div></li><li><div class="para">
<code class="filename">/usr/share/doc/pam-<em class="replaceable"><code><version-number></code></em>/txts/README.pam_timestamp</code> — Contains information about the <code class="filename">pam_timestamp.so</code> PAM module, where <em class="replaceable"><code><version-number></code></em> is the version number of PAM.
</div></li></ul></div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-PAM_and_Device_Ownership-Application_Access.html"><strong>Prev</strong>2.4.7.2. Application Access</a></li><li class="up"><a accesskey="u" href="#"><strong>Up</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Home</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Additional_Resources-Useful_PAM_Websites.html"><strong>Next</strong>2.4.8.2. Useful PAM Websites</a></li></ul></body></html>
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/></a><a class="right" href="http://docs.fedoraproject.org"><img src="Common_Content/images/image_right.png" alt="Documentation Site"/></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Sample_PAM_Configuration_Files.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-PAM_and_Administrative_Credential_Caching.html"><strong>Next</strong></a></li></ul><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title" id="sect-Security_Guide-Pluggable_Authentication_Modules_PAM-Creating_PAM_Modules">2.4.5. Creating PAM Modules</h3></div></div></div><a id="d0e6602" class="indexterm"/><div class="para">
You can create or add new PAM modules at any time for use by PAM-aware applications.
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For example, a developer might create a one-time-password creation method and write a PAM module to support it. PAM-aware programs can immediately use the new module and password method without being recompiled or otherwise modified.
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This allows developers and system administrators to mix-and-match, as well as test, authentication methods for different programs without recompiling them.
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Documentation on writing modules is included in the <code class="filename">/usr/share/doc/pam-<em class="replaceable"><code><version-number></code></em>/</code> directory, where <em class="replaceable"><code><version-number></code></em> is the version