Re: Snort with an expert system

["Stuart Staniford" <sstaniford () FireEye com>]

On Jun 25, 2009, at 5:18 PM, Gary Halleen wrote:

> 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.

To echo what Greg said - from a customer perspective, it's all the  
same.  Customers generally buy both an engine and a set of rules as a  
single package, and if the combination is reporting things that aren't  
actual attacks, then it's making them unhappy.  Few customers are  
writing their own rules.

Distinguishing between whether the problem is in the engine or the  
rule is useful internally at the vendor to decide what needs to get  
fixed, but customers are not likely to care that much.

The way our (FireEye's) technology reduces false positives is to  
replay the traffic in an instrumented virtual machine, to see if it  
really is an attack or not.  We have a lot fewer false positives than  
traditional IDS products (we don't ship a release with any that are  
known to us, though a few still pop up in the field unfortunately -  
you can never test against everything that will show up on a  
customer's network)

Stuart Staniford.

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