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Re: CVE request - mcrypt buffer overflow flaw
From: Raphael Geissert <geissert () debian org>
Date: Tue, 2 Oct 2012 17:52:12 -0500

On Tuesday 02 October 2012 14:20:20 Kurt Seifried wrote:
On 10/02/2012 12:42 PM, Raphael Geissert wrote:

I think at least one more CVE id needs to be assigned:

On Saturday 15 September 2012 19:22:06 Raphael Geissert wrote:
On Tuesday 11 September 2012 10:19:38 Eygene Ryabinkin wrote:

Another week, another couple of patches. One makes it use strncpy
and forces a NUL on the last byte of local_algorithm, local_mode,
and local_keymode. Their values are checked later on, so it seems
safe to pass unvalidated data. The size of the buffers is
hard-coded to avoid making many changes to the code.

I think this needs a separate id, since fixes were released by
Fedora and Debian referencing CVE-2012-4409 but only for the
original report.

Eygene's followup issues have been fixed in Debian without
referencing a CVE id.

Can you post a link to source fixes/commits? Thanks.

This is all there is:

The Debian changelog is probably not of much use.

Once those issues were fixed I noticed that salt_size is not
initialized if the salt flag is not set. The result is an
inconditional call to malloc, with an uninitialized int as
argument. This can lead to a non-attacker-controlled memory
consumption DoS in most cases. It makes me think nobody actually
ever used it without a salt.

I've no strong opinion on whether this deserves an id.


Hrmm there's a thought, has this DoS been confirmed? As we've probably
seen over the last year more than a few sites fail to salt their
stored passwords =(.

I don't see how that is relevant, this is the mcrypt(1) tool in concern. 
libmcrypt and libmhash are not affected.

The attached file is a PoC built with a slightly modified mcrypt. It appears 
that there is no way to disable the salt bit in the unmodified mcrypt while 
still producing a file that can later be opened. (for those looking at the 
code, the salt bit is only disabled when using --bare)

Raphael Geissert - Debian Developer
www.debian.org - get.debian.net

Attachment: foo.nc

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