Re: Snort with an expert system

[Gary Halleen <ghalleen () cisco com>]

On 6/25/09 3:26 AM, "Stefano Zanero" <s.zanero () securenetwork it> wrote:

> > "A false positive is an alert that triggers on normal traffic where no
> > intrusion or attack is underway"
>
> That's a good definition, but not really complete. Under that
> definition, if you place a rule that flags IRC connections, and it
> fires, is that a false positive?

GH:  No.  If a rule or signature fires on traffic you asked it to fire on,
then it is not a false positive, regardless of whether or not it is an
attack or intrusion.


> Is it a false positive a case where there is no rule, or the traffic
> does not match with the rule, and the engine still fires?

GH:  Yes.

 
> Is it a false positive a case where a rule correctly matches, but the
> user didn't want to be alerted to that traffic ?

GH:  Some say yes, some say no.  I am one of those who says this is not a
false positive.  Perhaps this is a misconfiguration of the sensor, but it is
still doing what it was asked to do.  I wrote "Security Monitoring with
CS-MARS" for Cisco Press, and that product considers this to be a false
positive.

Stay Secure!
Gary

Gary Halleen, CISSP-ISSAP, CHP
Author, Security Monitoring with CS-MARS, ISBN: 1587052709



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