Re: Announcement: Alert Verification for Snort

From: Martin Roesch (roesch_at_sourcefire.com)
Date: 10/24/03

  • Next message: Randy Taylor: "Re: Announcement: Alert Verification for Snort" 
    Date: Thu, 23 Oct 2003 21:51:54 -0400
To: "Raistlin" <raistlin@gioco.net>

    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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