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Re: mod_ssl Buffer Overflow Condition (Update Available)
From: Ben Laurie <ben () algroup co uk>
Date: Fri, 01 Mar 2002 09:54:41 +0000

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.

--
http://www.apache-ssl.org/ben.html       http://www.thebunker.net/

"There is no limit to what a man can do or how far he can go if he
doesn't mind who gets the credit." - Robert Woodruff


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