Re: Sourcefire VRT Certified Snort RulesUpdate2010-03-17

[Frank Knobbe <frank () knobbe us>]

On Tue, Mar 23, 2010 at 09:04:06PM -0500, evilghost () packetmail net wrote:
> > In my opinion, first off, it's CPU intensive. These days CPU's have gotten
> > faster where this is actually feasible. But several years ago, when we first
> > discussed this on the list (search snort-users archives, my guess would be
> > around 2004 time-frame, if not earlier), systems weren't quite fast enough
> > to keep up with the load. 
>
> IDS must evolve with threats.  2004?  We're now six years later.  Talk 
> about code stagnation.  It's bad enough we don't have SMP support.

Then why aren't you asking for a Javascript decoder plugin?

> So I have two choices; 1) Disregard all gzip encoded data in the hopes 
> that I don't encounter an overload situation and I might miss some data 
> while at the same time missing a crapton of data, or, 2) BPF, flow-pin, 
> and size my IDS according to my traffic volume to handle gzip encoded 
> data like I currently am forced to do because Snort doesn't support SMP 
> either.

I can see where your happyness about gzip might lead you to a false sense
of security (at the cost of CPU). Again, what about SSL? Javascript de-
obfuscation?

> Lets start with gzip first, then move forward.  It looks like if I'm 
> able to decode things that HTTPDs do now I'm be a a rock-star.

Okay, so once that's done, you'll be back complaining about the missing
email attachment unzipper/decoder?

> The current security threat tends to be client infection with the 
> majority of C&C being HTTP due to egress firewall avoidance.  It seems 
> the best way for me, should I be a malware author, would be to use 
> HTTP/1.1 with gzip encoding.  The end-point HTTPd won't have any 
> problems handing it.  I can count on one hand the the number of things 
> non-HTTP signatures catch versus HTTP/client signatures.

They use it today! I'm sure they have been for a couple years. Ever wondered
why most ET sigs dealing with malware are looking at the URI's instead of
the data portion?

> This is *how* we detect infected workstations since aside from a decent 
> HIPS, AV is a great placebo.

No, you're detecting attempts. I could care less if Snort is able to unzip
a web page delivering yet another FakeAV that doesn't stick on the workstation.
I prefer to look to the actual infection, focusing on what the workstation
does next. But we probably have different approaches to that angle, so there's
no point in taking that further.

Cheers,
Frank


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