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Network Security Snort-Signatures
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Re: [Snort-sigs] (no subject)

Subject: Re: [Snort-sigs] (no subject)
Date: Sun, 28 Nov 2004 11:17:04 -0500
On Nov 27, 2004, at 8:10 PM, warwick ackfin wrote:
Thanks to both you and Jason.  I have been playing with this for a
while and the not operator doesn't seem to be working for me.

Here's what I'm using:

         alert icmp $EXTERNAL_NET any -> $HOME_NET any (msg:"my ICMP alert";
icode:0; itype:8; content:!"ABCDEFGHIJKLMNOPQRSTUVWABCDEFGHI";)

This is due to the fast pattern match engine. From what I understand, it was non-trivial to add support for negative content matching into the FP engine. Unfortunately, marc & dan didn't add support to use content as a regular detection plugin if it was a single not.


Oh well.

You can cheat by using a negative pcre statement instead of a negative content. It isn't as fast, but hey, it works.

pcre:!"/ABCDEFGHIJKLMNOPQRSTUVWABCDEFGHI";

Brian



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