[Snort-sigs] RE: [Snort-users] Who doesn't care about virus rules, and why?

Abe Use neosporin1v1 at ...125...
Fri Nov 7 05:54:15 EST 2003

Symantec writes great rules for IDS such as snort.
or they have enough of the worm/virus documanted to write a good alert

the've done better work like this

(about 3/4 the way down tha page begins the IDS sig for bugbear)

I believe they provide these for thier ManHunt software, however, they 
easily work in SNORT.

Granted they don't always have them for every virus, but if you could 
decipher their ManHunt rules, you may get a better place to start!

(these too seem out of date...)

Your best bet, write your own. Get ethereal or windump- find a infected 
machine- isolate it that pc, and watch it's traffic. Look for unique 
behaviour and or data- try try again...
-----Original Message-----
From: Williams Jon [mailto:WilliamsJonathan at ...2134...]
Sent: Thursday, November 06, 2003 8:36 AM
To: kenw at ...10492...; snort-users at lists.sourceforge.net
Cc: snort-sigs at lists.sourceforge.net
Subject: [Snort-sigs] RE: [Snort-users] Who doesn't care about virus
rules, and why?

While I agree that IDS plays a role in tracking down virus-infected 
machines, I have to agree that most of the rules specifically written to 
detect virus traffic aren't of much use.  My reasons, though, are probably 
different from what others think.

Over the past several months, I've been amazed at the amount of time spent 
trying to come up with the "correct" signature for Blaster/Welchia/whatever. 
  While it is true that we can write fairly specific rules to detect these 
things, those specific rules will almost never trigger, particularly in a 
large network that is only sparsely populated.

The majority of worms that I've seen, with the notable exception of 
SQLSlammer, are TCP-based.  They also use a randomization technique to 
spread beyond their local subnet.  What this ends up meaning is that 
something like 90% of the time (in networks I monitor), the worm tries to 
connect to non-existant or unreachable IP addresses.  In these cases, if 
you're only looking for the worm-specific data within the session, your 
rules won't trigger - all that passes the sensor (if anything) is the TCP 
SYN packet and maybe a TCP RST.

What we've ended up doing is monitoring the default route path for our 
network and watching for either TCP SYNs that are going places they 
shouldn't or TCP RST packets generated either by the firewall or the odd 
host that is actually hit.  With thresholding, we can generate fairly useful 
alerts in cases where, in Blaster's case, one source address sends out TCP 
port 135 SYN packets to more than X number of hosts in Y period of time.  
This is so reliable, in nearly every case we've used it on, that we are able 
to auto-generate email alerts that go to someone else to actually _deal_ 
with the problem rather than making the IDS staff track down and call each 
victim independantly.

Of course, we also have content-specific rules, but they rarely fire and the 
don't catch varients.  The thresholded behaviour rules have been catching 
both varients of what we were trying to find and propegation activity from 
worms we didn't know about.

So, to answer your question, if you've got a place where all your junk 
traffic goes (i.e. your main Internet connection) _and_ you don't allow the 
protocol out, such as with MSRPC stuff on 135, 137, 139, 445, etc., run a 
simple set of rules looking for those SYN packets outbound and use the 
thresholding thing if you can.  I think you'll find it more useful than the 

Good luck.


-----Original Message-----
From: kenw at ...10492... [mailto:kenw at ...10492...]
Sent: Wednesday, November 05, 2003 9:45 PM
To: snort-users at lists.sourceforge.net
Subject: [Snort-users] Who doesn't care about virus rules, and why?

The header of virus.rules says:

># NOTE: These rules are NOT being actively maintained.
># These rules are going away.  We don't care about virus rules anymore.

Who are "we", and what makes them think these rules aren't important?

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