Marty,
Thanks for laying out all eight possibilities (your numbers 3 and 6 each
representing two each). I have seen a lot of text written to this list
trying to get at the difference between an attack one cares about and an
attack one doesn't care about. I agree that the latter is still an
attack, it's "ineffective" or something, but it's impact on a given
network is different than it's intent (which is to attack).
Would you care to suggest a succinct way (word or phrase) we can agree
to use to describe a true but ineffective attack? (They are two
different dimensions, and perhaps explicitly giving a new name here
would help get over the red herring of whether an attack that has no
impact is an attack.)
Thanks,
Aaron
Aaron Temin
Ringneck Technologies
On Wed, 2003-10-22 at 23:22, Martin Roesch wrote:
> Hi Chris,
>
> Just to make a point of semantics, I'd like to comment on the "reduce
> the large number of false positives produced by intrusion detection
> systems such as Snort" quote from your post.
>
> I spent some time a couple months ago talking about the misconceptions
> of "false positives" in Snort on this very list and I think there's a
> valid point to be made here. Let me enumerate the cases you can have
> as I see it:
>
> 1) Detect, Attack Present, Vulnerable: True Positive
> 2) Detect, Attack Present, Not Vulnerable: Nontextual (i.e. detect
> requiring contextual data to resolve)
> 3) Detect, No Attack, [vuln|not vuln]: false positive
> 4) No Detect, Attack Present, Vulnerable: False Negative
> 5) No Detect, Attack Present, Not Vulnerable: ?
> 6) No Detect, No Attack, [vuln|not vuln]: Don't care (true negative?)
>
> In case 2 the "nontextual" isn't a false positive but I think that most
> people are calling it an FP these days. I *personally* think that's a
> misconception. What we have in that case is a *real attack* that your
> IDS is detecting exactly as it was asked to. Just because it doesn't
> have the additional information about the context or relevance of the
> event isn't a problem with the IDS, it's a side effect of the way that
> NIDS have been built for the past 10 years.
>
> Case 3 is where we have the true false positives, the NIDS is detecting
> attacks that aren't occuring on the network. I think that case 2
> happens far more than case 3 with systems like Snort, which is why I
> think it's important to make the distinction between "real" false
> positives (i.e. the IDS screwed up) and nontextuals where the IDS has
> done its job, it just needs more information to properly evaluate the
> reality and priority of the event.
>
> I hope this is making sense to everyone here, please let me know if you
> have any questions. Looks like a neat tool Chris!
>
>
> -Marty
>
> On Oct 21, 2003, at 9:16 PM, Christopher Kruegel wrote:
>
> > [Please excuse multiple copies of this message]
> >
> > Alert Verification is a technique to reduce the large number of false
> > positives produced by intrusion detection systems such as Snort. The
> > idea is to actively probe for the vulnerability that is exploited by a
> > certain detected attack. When the victim is not vulnerable, the alert
> > can be simply discarded or tagged with a low priority.
> >
> > William Robertson has implemented an extension for Snort that
> > implements Alert Verification. Patches for the current version of
> > Snort (2.0.2) and additional information are available under
> >
> > http://www.cs.ucsb.edu/~wkr/projects/ids_alert_verification/
> >
> >
> > Please send any comments or bug reports to
> >
> > snort-av_at_cs.ucsb.edu
> >
> >
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Received on Oct 23 2003
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