proxy_ssl_certificate not exchanging client certificates

[Maxim Dounin]

Hello!

On Wed, Apr 29, 2015 at 05:09:26PM -0400, lieut_data wrote:

> Thanks for getting back to me so quickly!
> 
> Maxim Dounin Wrote:
> -------------------------------------------------------
> > What nginx doesn't support (or, rather, explicitly forbids) is 
> > renegotiation.  On the other hand, renegotiation is required if 
> > one needs to ask for a client certificate only for some URIs, so 
> > it's likely used in your case.  You should see something like "SSL 
> > renegotiation disabled" in logs at notice level.
> 
> Yes, this is exactly the problem. With your hint, I commented out the
> relevant code in ngx_ssl_handshake and ngx_ssl_handle_recv -- and proxying
> worked flawlessly. (Interestingly, I never saw the log you identified
> because of SSL3_FLAGS_NO_RENEGOTIATE_CIPHERS having been set on the openssl
> connection object.)
> 
> I think I understand the gist of why nginx forbids client-initiated
> renegotiation (denial of service concerns? security concerns?), but I'm not
> well-versed in openssl enough to know if the same concerns apply to
> server-initiated renegotiation with nginx as the client, especially when it
> applies to cipher renegotiation as noted above.
> 
> Would nginx be open to a patch that would make this use case feasible?
> Perhaps as a modification to only disable these renegotiations when nginx is
> the server in the SSL equation?

The renegotiation is disabled for security reasons since 
CVE-2009-3555.  While CVE-2009-3555 is believed to be mitigated by 
Secure Renegotiation extension, renegotiation itself, even secure, 
still allows various bad side effects if allowed: in particular, 
peer credentials and/or ciphers used may be changed unexpectedly.

I don't think we care much about the above happening on an 
upstream connection though, so patches are welcome.  (Actually, 
original patch I submitted back in 2009 did not touch upstream 
connections at all, but Igor decided to disable renegotiation 
completely.)

-- 
Maxim Dounin
http://nginx.org/