"Invalid IV size (16) for CBC" when retrieving from vaults via RHEL 9 server

[Sam Morris]

I've added a RHEL 9 server to my IPA domain and I am finding that 'ipa 
vault-retrieve' fails intermittently.

It turns out that whenever the ipa client talks to the RHEL 9 server, 
this error happens:

$ ipa vault-retrieve --service host/myhost.example.com manager-password
Traceback (most recent call last):
   File "/usr/lib/python3/dist-packages/ipalib/backend.py", line 141, in 
execute
     return self.Command[_name](*args, **options)
   File "/usr/lib/python3/dist-packages/ipalib/frontend.py", line 471, 
in __call__
     return self.__do_call(*args, **options)
   File "/usr/lib/python3/dist-packages/ipalib/frontend.py", line 499, 
in __do_call
     ret = self.run(*args, **options)
   File "/usr/lib/python3/dist-packages/ipalib/frontend.py", line 1229, 
in run
     return self.forward(*args, **options)
   File "/usr/lib/python3/dist-packages/ipaclient/plugins/vault.py", 
line 1069, in forward
     vault_data = self._unwrap_response(
   File "/usr/lib/python3/dist-packages/ipaclient/plugins/vault.py", 
line 1021, in _unwrap_response
     cipher = Cipher(algo, modes.CBC(nonce), backend=default_backend())
   File 
"/usr/lib/python3/dist-packages/cryptography/hazmat/primitives/ciphers/base.py",

line 97, in __init__
     mode.validate_for_algorithm(algorithm)
   File 
"/usr/lib/python3/dist-packages/cryptography/hazmat/primitives/ciphers/modes.py",

line 85, in _check_iv_and_key_length
     _check_iv_length(self, algorithm)
   File 
"/usr/lib/python3/dist-packages/cryptography/hazmat/primitives/ciphers/modes.py",

line 69, in _check_iv_length
     raise ValueError(
ValueError: Invalid IV size (16) for CBC.
ipa: ERROR: an internal error has occurred

I can reproduce this both on Debian unstable (with ipalib 4.9.8-1) and 
RHEL 8. I do this by overriding the value of xmlrpc_uri in 
/etc/ipa/default.conf to point to the RHEL 9 server before running 'ipa 
vault-retrieve'.

If I run the command on the RHEL 9 server, it works fine. I don't have a 
RHEL 9 client to test with.

-- 
Sam Morris <https://robots.org.uk/>
PGP: rsa4096/CAAA AA1A CA69 A83A 892B  1855 D20B 4202 5CDA 27B9

[Rob Crittenden]

Sam Morris via FreeIPA-users wrote:
>  I've added a RHEL 9 server to my IPA domain and I am finding that
> 'ipa
>  vault-retrieve' fails intermittently.
>  
>  It turns out that whenever the ipa client talks to the RHEL 9 server,
>  this error happens:
>  
>  $ ipa vault-retrieve --service host/myhost.example.com manager-password
>  Traceback (most recent call last):
>    File "/usr/lib/python3/dist-packages/ipalib/backend.py", line 141, in
>  execute
>      return self.Command[_name](*args, **options)
>    File "/usr/lib/python3/dist-packages/ipalib/frontend.py", line 471, in
>  __call__
>      return self.__do_call(*args, **options)
>    File "/usr/lib/python3/dist-packages/ipalib/frontend.py", line 499, in
>  __do_call
>      ret = self.run(*args, **options)
>    File "/usr/lib/python3/dist-packages/ipalib/frontend.py", line 1229,
>  in run
>      return self.forward(*args, **options)
>    File "/usr/lib/python3/dist-packages/ipaclient/plugins/vault.py", line
>  1069, in forward
>      vault_data = self._unwrap_response(
>    File "/usr/lib/python3/dist-packages/ipaclient/plugins/vault.py", line
>  1021, in _unwrap_response
>      cipher = Cipher(algo, modes.CBC(nonce), backend=default_backend())
>    File
>
> "/usr/lib/python3/dist-packages/cryptography/hazmat/primitives/ciphers/base.py",
>  line 97, in __init__
>      mode.validate_for_algorithm(algorithm)
>    File
>
> "/usr/lib/python3/dist-packages/cryptography/hazmat/primitives/ciphers/modes.py",
>  line 85, in _check_iv_and_key_length
>      _check_iv_length(self, algorithm)
>    File
>
> "/usr/lib/python3/dist-packages/cryptography/hazmat/primitives/ciphers/modes.py",
>  line 69, in _check_iv_length
>      raise ValueError(
>  ValueError: Invalid IV size (16) for CBC.
>  ipa: ERROR: an internal error has occurred
>  
>  I can reproduce this both on Debian unstable (with ipalib 4.9.8-1) and
>  RHEL 8. I do this by overriding the value of xmlrpc_uri in
>  /etc/ipa/default.conf to point to the RHEL 9 server before running 'ipa
>  vault-retrieve'.
>  
>  If I run the command on the RHEL 9 server, it works fine. I don't have a
>  RHEL 9 client to test with.
>   
It seems to be an interop problem between the server and client. The
RHEL 9 server is wrapping the secret with AES but the client is trying
to use TripleDES (and only supports 3DES).

Upstream ticket https://pagure.io/freeipa/issue/6524 changed from a
hardcoded wrapping algorithm to be more flexible but this is apparently
not backwards compatible.

I'm not deeply familiar with this wrapping code so I don't know if there
is a workaround yet.

Any chance you can file a RHEL-8 bug against ipa for this while I
continue looking?

thanks

rob

[Sam Morris]

On 21/06/2022 19:45, Rob Crittenden wrote:
>  It seems to be an interop problem between the server and client. The
>  RHEL 9 server is wrapping the secret with AES but the client is trying
>  to use TripleDES (and only supports 3DES).
>  
>  Upstream ticket https://pagure.io/freeipa/issue/6524 changed from a
>  hardcoded wrapping algorithm to be more flexible but this is apparently
>  not backwards compatible.
>  
>  I'm not deeply familiar with this wrapping code so I don't know if there
>  is a workaround yet.
>  
>  Any chance you can file a RHEL-8 bug against ipa for this while I
>  continue looking?
>  
>  thanks
>  
>  rob 
Thanks Rob, here you go

https://bugzilla.redhat.com/show_bug.cgi?id=2100115

-- 
Sam Morris <https://robots.org.uk/>
PGP: rsa4096/CAAA AA1A CA69 A83A 892B  1855 D20B 4202 5CDA 27B9