Re: How to write a rule file to detect land-attack, syn-flood

[Erek Adams <erek () theadamsfamily net>]

On Wed, 20 Feb 2002, Prerana Sharma wrote:

> I am trying to learn Snort. And I am really confused
> with the documentation. So, could someone please tell
> me how to write a very simple rule file to detect a
> land-attack and a syn-flood.

You can't.

Snort works on a 'packet grep' style of detection.  "Check this packet, does
it match X, Y and Z?   Great, trigger Alert QQZ.  If not, skip it and go on to
the next one."

To detect land/syn floods, you would have to write a pre-processor that would
keep up with incoming syn's and flag when it hit a certain level.  You might
look at the code for spp_portscan.{c,h} to see something like that in action.

Hope that helps!

-----
Erek Adams
Nifty-Type-Guy
TheAdamsFamily.Net


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