[Snort-users] Writing a "not" snort rule

ntbuck12 at ...131... ntbuck12 at ...131...
Tue Mar 19 14:44:26 EDT 2013


Thanks! I hadn't seen that used outside of an IP context. I needed that keyword to find the info I wanted. Thanks!

For those interested - The content below is stolen from the snort manual.
http://www.snort.org/assets/166/snort_manual.pdf

A ! modifier negates the results of the entire content search, modifiers included. 
For example, if using content:!"A"; within:50;and there are only 5 bytes of payload 
and there is no ”A” in those 5 bytes, the result will return a match. 
If there must be 50 bytes for a valid match, use isdataat as a pre-cursor to the content.




________________________________
 From: JJC <cummingsj at ...11827...>
To: ntbuck12 at ...131... 
Cc: "snort-users at lists.sourceforge.net" <snort-users at lists.sourceforge.net> 
Sent: Tuesday, March 19, 2013 2:35 PM
Subject: Re: [Snort-users] Writing a "not" snort rule
 
He probably gets payed way too much already, this "Joe" character ;-)

On a serious note, do a search in the snort_manual for the keyword
"negate" and around page 182, and other locations, you will find your
solution.

JJC

On Tue, Mar 19, 2013 at 12:30 PM,  <ntbuck12 at ...131...> wrote:
> Attention Joe and snort rule writers. I have read a fair amount of
> information on writing rules, but now I am stuck on how to to this.
>
> How could I detect on the following scenario? - Alert on any packet that
> contains ANYTHING OTHER THAN "message1", "message2" or "message3", in a
> certain field.
>
> Obviously I could use offset and depth to narrow down to the field I'm
> looking at, but now to a do a "negative search". Ideas?
>
>
> Side Note: I'm pretty sure whatever Joe Esler gets paid isn't nearly enough.
> I love the blogs too, Joe.
>
>
>
>
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