[Python-Dev] OpenSSL vulnerability

Bill Janssen janssen at parc.com
Fri Nov 6 23:18:22 CET 2009


Guido,

I'm working from <http://extendedsubset.com/Renegotiating_TLS.pdf>.

I believe geremy is right.  The current SSL module does not expose much
of the SSL API, so servers implemented in Python, using it, should
(fortuituously) be immune to the some of the attacks outlined, simply
because there's no way to do an application-initiated renegotiation,
which the first two scenarios presuppose.  On the other hand, there's no
way to do application-directed session resumption, either, which might
be a good add to support new or updated application protocols which
address this problem.

So I think there's not much we can do in Python source code to address
this, unless there's a switch we can throw in the existing OpenSSL API
to turn off renegotiation completely.  I'll look, and I'll talk this
over with our security group.  Building binaries with newer versions of
OpenSSL is pretty much always a good idea, it seems to me.

More generally, this is a nice description of how simply layering TLS
onto existing application protocols like HTTP doesn't always work very
well.

Bill


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