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Re: .exe
From: waldo kitty <wkitty42 () windstream net>
Date: Sat, 04 May 2013 22:25:31 -0400

On 5/4/2013 16:34, tarik shalo wrote:
Hi,

I had to collect and put your responses from the mailing list into this
email, because I didn't get the reply messages in my email.

i don't know how others do it but i only reply to the list unless special 
circumstances are in play... you should be getting all messages from the list... 
if you aren't, you might want to check our spam bucket ;)

Anyway, What I was trying to accomplish was to write a rule that fires when
executable files are downloaded from any web server. For that, I put .exe
file in a web server and requested that file via httpfrom the machine that
runs Snort. After removing the"flow:to_server,established"  from the rule,
the rule fired but from your responses, I think I was not doing it the right
way. Could you suggest me a better way?

well, the thing is that detecting the extension is not going to be complete... 
you need to detect the binary signature(s)... some DOS/Winwhatever EXEs start 
with MZ while most of todays stuff starts with PE but there's a bit more to it 
than just that...

additionally, it is not just a "content" detection anywhere like in headers 
which your rule would catch... VRT has numerous rules which work for detecting 
items like this... in particular, the file-executable.rules which set flowbits 
(without an alert) indicating that such a file was detected and then other rules 
are used to detect if the flowbit is set as well as looking at other aspects of 
the data to determine if an alert should be fired for policy violations or 
malware or such...

so basically, you cannot detect an EXE file simply by looking for ".exe" in the 
traffic... you have to detect the signature of an executable binary... that 
means looking inside binary files to see what is uniform to be used for detection...

Also, in which rule files are the emerging threat rules 2000419 and 2015744?

those are in the Emerging Threats rules set... it is distributed by Emerging 
Threats and completely separate from the VRT rules...

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