[Snort-users] Klez sig detects Frethem-Fam

Shane Williams shanew at ...5387...
Tue Jul 16 06:49:12 EDT 2002


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I've been using the following rule for a couple of months, and I
haven't seen any false positives (I'm also using it as a system-wide
procmail filter and I check for false positives there), but I'm not
familiar with Frethem-Fam, so maybe I just don't realize.

I purposely put in some of the carriage returns so it's less likely to
set off people's filters.  Note also that I want to know if it's
leaving my network as well as coming in.

# Catch Klez in SMTP
alert tcp any any -> any 25 (msg:"Virus - Klez"; 
content:"135AAItEjhyJRI8ci0SOGI
lEjxiLRI4UiUSPFItEjhCJRI8Qi0SODIlEjwyLRI4IiUSPCItE"; sid:10012;
classtype:misc-activity; rev:1;)

If you get either false negatives or positives, please let me know.

On Tue, 16 Jul 2002, Detmar  Liesen wrote:

> Hi again,
> granted, I haven't read my sigs mail thoroughly during the past few days, so
> maybe this has already been discussed.
> 
> We are currently detecting lots of "Klez" worms with our snort, which are in
> fact Frethem-Fam worms, so the two seem to be related or derived from each
> other.
> I can tell this from the AV alerts on our mail gateway.
> 
> Question:
> Is there any means to distinguish the two from each other?
> I'd rather not look for the "password" W8dqwq8q918213 (see reference
> in-line)  
> since this is likely to change. 
> Has anybody created a sig for Frethem already?
> 
> Maybe it's no good to create additional signatures for each derived worm,
> because this
> has negative impact on snort performance. Snort is no AV tool anyway.
> 
> What do you recommend regarding worm/virus detection in snort?
> Is this something we should leave to the AV software solely?
> 
> TIA,
> Detmar
> 
> Additional Info:
> http://www.sophos.com/virusinfo/analyses/w32frethemfam.html
> 
> 

- -- 
Public key #7BBC68D9 at            |                 Shane Williams
http://pgp.mit.edu/                |                               
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All syllogisms contain three lines |              shanew at ...5387...
Therefore this is not a syllogism  |   www.gslis.utexas.edu/~shanew

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