I just found an email thread about this exact subject back in May of 05.

http://archives.neohapsis.com/archives/sf/ids/2005-q2/

Joel

2009/3/13 tanyoo10 <tanyoo10 (at) 163 (dot) com [email concealed]>
>
> Greetings to everyone.
>
>  I have some questions about exploit-based and vulnerability-based signature of IDS.
>
>  I heard that exploit-based signature is dead (useless), since vulnerability-based signatures are more effective than exploit-based signatures in that they can detect unknown exploits if a vulnerability can be utilized by many exploits. However, I don't agree with this argument, for the following reasons:
> (1) When a vulnerability is unknown, exploit-based might be a good solution.
> (2) Exploit-based signatures are still irrepetable for early defense of zero-day worms or zero-day exploits, since exploit-based signatures can be generated more timely.
> (3) In the perfect world, we need to generate both types of signatures (even finally we only use vulnerability-based signature in detection). That way we not only know we were attacked, but we know with what type of exploit; or that it's a new unknown variant of an exploit. That's useful information in and of itself.
>
>        To support the above viewpoints, I have some concrete questions needed to be answered:
> (1) Were there some attacks that have exploit-based signature but have not vulnerability-based signature? Can someone give me some exmples?
> (2) Were there some examples to show that exploit-based signatures were generated much quickly and timely than the generation of vulnerability-based signatures for the historical worms or attacks ?
> (3) Does current IDS (e.g. Snort) use both signature types of exploit-based and vulnerability? If so, what percentage of sigantures are exploit-based?
>
>
> Thanks for you any input of discussing "exploit-based vs. vulnerability-based signature" !
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