Re: mod_ssl Buffer Overflow Condition (Update Available)

[Ben Laurie <ben () algroup co uk>]

Ed Moyle wrote:
> MITIGATING FACTORS
>
> This vulnerability is unlikely to be exploitable in a production
> environment. Since the buffer in question is the contents of the
> SSL session, exploitability of this scenario would be tied to
> increasing the size of the session.  The most obvious way of doing
> this would be through the use of client certificates.  Therefore,
> generating a really big client cert would overflow the buffer, and
> could potentially be used to run arbitrary code.  HOWEVER, these
> routines are only called AFTER SUCCESSFUL VERIFICATION of the client
> cert, which would mean that a CA *TRUSTED BY THE WEB SERVER* would have
> to issue the certificate in question.  In addition, both client cert
> auth and the dbm or shared memory session caching functionality would
> need to be enabled.

This analysis is flawed: although the certificate would have to be
issued by a trusted CA, some parts of the certificate are under control
of the owner of the certificate, who could therefore get a certificate
of arbitrary size by, for example, requesting a very large DN. I can see
no reason that a CA would vet CSRs for size - why should they? So, the
fact that a trusted CA produced the certificate has no bearing on its
size.

Cheers,

Ben.

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