The problem is that there is no guaranteed offset, the COM(comment)
section can be right after SOI (start of image) or after the JFIF
marker, if there is one, etc... And the JFIF marker itself can be
65535 bytes in length.
I wrote one that looks for the SOI, COM and Huffman table start and I
still get lots of false positives, I have yet to find a good way to
eliminate false positives. There is alot of flexibility in the
formatting of a jpeg and that makes this difficult.
On Tue, 21 Sep 2004 09:57:22 +0100, Chas Tomlin <cet@ecs.soton.ac.uk> wrote:
Hi,
I'm using these rules to spot malicious jpegs.
alert tcp $EXTERNAL_NET $HTTP_PORTS -> $HOME_NET any (msg:"WEB-CLIENT
jpeg vulnerability"; flow:to_client,established; content:"Content-Type\:
image/jpeg"; content:"|FF FE 00 00|"; classtype:attempted-user;
sid:3000363; rev:10;)
alert tcp $EXTERNAL_NET $HTTP_PORTS -> $HOME_NET any (msg:"WEB-CLIENT
jpeg vulnerability"; flow:to_client,established; content:"Content-Type\:
image/jpeg"; content:"|FF FE 00 01|"; classtype:attempted-user;
sid:3000363; rev:10;)
So far I haven't seen any, just a few false positives. I think the rules
could be improved by specifying an offset for the COM length (00 0)/00
01).
Chas
-----Original Message-----
From: snort-sigs-admin@lists.sourceforge.net
[mailto:snort-sigs-admin@lists.sourceforge.net] On Behalf Of Frank
Knobbe
Sent: 20 September 2004 18:07
To: snort-sigs@lists.sourceforge.net
Subject: [Snort-sigs] JPEG / GDI+ DLL exploit sig?
Greetings,
it seems there are now three Proof-of-Concept exploits out for the JPEG
handling issue in the GDI+ DLL (MS04-028).
Does anyone have a signature for this yet? Preferable on the problem
(like the libpng issue) and not just pattern match on the exploits.
Cheers,
Frank
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