Re: on NIDS/NIPS tuning

["Drew Simonis" <simonis () myself com>]

> All,
>
> I was thinking about some issues with IDS alerts (their volume, etc) and
> realized I could use some help from the list. It might also be a  fun
> discussion item.
>
> So, here it is: how many folks who buy/download a NIDS/NIPS actually tune
> it? Long time ago when I was asking this question the previous time, I was
> scared to learn that lots of people do not tune their NIDSs. Is it any
> better now?

I know that, in my experience, many orgs don't tune at all.  The fear is 
that they might do it wrong and thereby miss some important event.  IMO,
this is a stupid way of thinking, but I bet it isn't as rare as it should
be.  

In other cases, people do not tune and rely on a correlation engine or MSS
to filter the events.  This is better, but really just moves the tuning to 
a different level.

Personally, I tune sigs and also tailor the sig sets to the devices being
monitored.  For example, if there are no webservers on a segment, I might
not be as inclined to use sigs that check for Apache exploits.  I've never
really measured the impact on the system vs. the administrative cost of 
doing this, however, so it is quite possible I am wasting time for a 
negligable benefit.  

On the tuning side, I believe that filters and exclusions should be part
of the incident response lifecycle.  If I am alerted to an event by an IDS,
I investigate and discover that the event was benign or did not take place,
a filter should result, and thus be properly documented.  

-Ds

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