full-disclosure - Analysis of a Spam Trojan

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From: jstewart at lurhq.com (Joe Stewart)
Subject: Analysis of a Spam Trojan

On Thu, 25 Sep 2003 12:04:14 -0500, Brian Eckman wrote:
> It is unknown how the audio.exe file got onto the computer hard drive 
> in the first place.

It is almost guaranteed to have been via the MS03-032 IE object tag 
vulnerability. The trojan you found is a variant of the Autoproxy 
trojan, which has been known to use that infection vector on a large 
scale. Some AV companies detect it as Coreflood because it shares a lot 
of the same code, likely because it is by the same author. You are 
correct in your analysis that it is not a DDoS bot, but instead is a 
spam tool. Here is an analysis I did on a recent variant that uses a 
different master server and contacts cnet.com instead of microsoft.com:

http://www.lurhq.com/autoproxy.html

Here is another Snort signature you can use to detect when an infected 
user attempts to contact its controlling server:

alert tcp $HOME_NET any -> $EXTERNAL_NET 80 (msg:"Autoproxy Trojan 
control connection"; content: "|0d 0a 55 73 65 72 2d 41 67 65 6e 74 3a 
20 41 75 74 6f 70 72 6f 78 79 2f|"; classtype:trojan-activity; 
sid:1000028;  rev:1;)

It is interesting to note the connection between the DDoS trojan and the 
spam-proxy trojan here, in light of the recent DDoS attacks on spam 
blackhole lists.

-Joe

-- 
Joe Stewart, GCIH 
Senior Security Researcher
LURHQ Corporation
http://www.lurhq.com/