Re: Announcement: Alert Verification for Snort

[Martin Roesch <roesch () sourcefire com>]

Hi Raistlin,

On Oct 23, 2003, at 6:35 AM, Raistlin wrote:

> > 1) Detect, Attack Present, Vulnerable:  True Positive
> > 2) Detect, Attack Present, Not Vulnerable: Nontextual (i.e. detect
> > requiring contextual data to resolve)
>
> Actually, I think that vulnerable or non-vulnerable is not tied to the
> true/false positive concept... so I'd say:
>
> Detect, Attack Present, Signature Present, [vuln|not]: True Positive

The "signature" (detection method) being present was implicit since 
there was a detection. :)

> (thinking of a signature based system, reword it for your favorite 
> system)
>
> > 4) No Detect, Attack Present, Vulnerable: False Negative
> > 5) No Detect, Attack Present, Not Vulnerable: ?
>
> Here it is a bit more complex, but I'd say
> No Detect, Attack Present, Signature Present, [Vuln|not vuln]: False
> Negative

I'm leaning that way as well, but I think I'd classify it as somewhere 
between a False Negative an a nontextual.  Some people might call it a 
fortunate happenstance since it reduces the data load from the IDS even 
if it is by mistake. :)

> No Detect, Attack Present, Signature Present, Not Vulnerable: a lucky 
> false
> negative :)

Exactly!

> > 6) No Detect, No Attack, [vuln|not vuln]: Don't care (true negative?)
>
> True negative is the correct definition, but it encloses also:
>
> No Detect, [Attack|No Attack], No Signature, [vuln|not vuln]

Yes.

> > 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.
>
> I agree wholeheartedly.

     -Marty

--
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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