Heads up: Disabling SSL2 support in NSS

Elio Maldonado emaldona at redhat.com
Wed Feb 11 16:38:48 UTC 2015

On 02/09/2015 08:22 AM, Florian Weimer wrote:
> On 02/09/2015 03:43 PM, Elio Maldonado wrote:
>> Support for ssl2 will be disabled in NSS. Refer to the to the Mozilla page with a list of sites [1] and the fedora bug [2] filed to disable SSL2 at build time. Upstream NSS will disable SSL2 perhaps as early as September of this year. Red Hat has had SSL2 disabled at built time since RHEL-7.0 which was released in the summer of last year. There have been no complaints so far. The plan was originally to disable it in Fedora but that wasn't possible as at that time which was late 2013. Then rhel-7.0 was about to enter beta but fedora 20 was late in the beta stage and it didn't seem prudent to introduce potentially disturbing changes so late in the development cycle. Now we can finally do it and is way in advance of when we may get it from upstream and gives packages maintainers sufficient of lead time to deal with any sites that may still be using SSL2.
> Out of curiosity, does this also disable processing of SSL 2.0
> compatible Client Hellos advertising a later protocol version, or will
> NSS just stop negotiating SSL 2.0?
Good question Florian and the answer is that we disable SSLv2 compatible 
hellos. This is from Bob Relyea:
SSL 2 hellos have to be disabled if you ever send any extensions, so ECC 
support, or TLS 1.2 support requires that you don't send SSL2 hellos. So 
the upshot is we only send SSL2 hellos if you explicitly turn them on 
and only use SSL2/SSL3 and no ECC. Mozilla hasn't been using SSL2 hellos 
for about a decade now.

Once I resolve some issues with Firefox, which oddly enough don't happen 
in RHEL, and the work reviewed I'll proceed disable SSL2 for Rawhide.


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