Hi Aaron,
I've been calling the "real attack, not vulnerable" detection case
"nontextuals" lately which is the one word way of saying "it was a real
attack that was contextually irrelevant against the target due to lack
of a suitable vulnerability existing on that target". :)
I've been calling them that for a few months now, people seem to get it
but maybe people at large on the focus-ids list and in industry won't
want to adopt it since I'm "a vendor" these days. I guess we'll see.
-Marty
On Oct 23, 2003, at 5:58 AM, Aaron Temin wrote:
> 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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>
>
--
Martin Roesch - Founder/CTO, Sourcefire Inc. - (410)290-1616
Sourcefire: Snort-based Enterprise Intrusion Detection Infrastructure
roesch@sourcefire.com - http://www.sourcefire.com
Snort: Open Source Network IDS - http://www.snort.org
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Received on Oct 24 2003
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