--On Saturday, March 14, 2009 01:58:22 +0100 Damiano Bolzoni
<damiano.bolzoni (at) utwente (dot) nl [email concealed]> wrote:

> On 13/03/2009 21.05, Paul Palmer wrote:
>
>> So, for example, in some (well, at
>> least one) IDS products, the signature writer can write a single
>> signature to recognize attempts to exploit a vulnerability in a data
>> structure embedded within a Quicktime Movie file even before he knows
>> how the attacker will encode the exploit.
>
> Paul, I think the IDS you're talking about is unique (so far), and I believe
> I know which one you're referring to :)
> To go back to Terry's question, Paul's example shows something that you
> cannot really do right now with Snort. You would need to rewrite the
> detection engine from scratch, in particular the regular expression engine (I
> won't mention the details, but the whole thing is related with grammar and
> automaton theory).
> We had a similar case when monitoring a network with an anomaly-based NIDS.
> Snort was able to detect only one instance of the attack, while the
> anomaly-based NIDS detected all the attack instances. To achieve the same
> detection rate with Snort, we should have written another 255 rules...which
> would have make the whole system just run slower (and to detect just one
> attack!)...
> Signature-based IDSs are moving towards vulnerability signatures, because
> their application is of great interest especially for IPS vendors. However,
> the power of vulnerability signatures has not been fully explored yet.

Unless you can be more specific, I'm going to call your claim bogus. It is
entirely possible to write one snort signature that will detect *every*
instance of an attempt to overflow a buffer in a particular applicaiton no
matter what the attack "signature" is. You just have to understand the snort
logic and syntax and understand packet analysis well enough.

Your comment seems based upon the run of the mill signatures routinely
submitted by average joe's trying to give back to the community.

And yes, I know exactly which IDS you're referring to. They also claim to have
the best vulnerability scanner on the market - one we found so useless we
trashed it after spending ridiculous amounts of money and insance amounts of
effort trying to get it to work. If that's any indication of how well their
IDS works, I wouldn't give it the time of day, much less a fair evaluation.

--
Paul Schmehl, Senior Infosec Analyst
As if it wasn't already obvious, my opinions
are my own and not those of my employer.
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