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Re: pcre high cpu usage
From: Tomas Heredia <tomas.heredia () activesec biz>
Date: Mon, 18 Oct 2010 19:57:40 -0300

 El 18/10/2010 07:27 p.m., Joel Esler escribió:
On Oct 18, 2010, at 5:51 PM, Tomas Heredia wrote:
Hi all!

Lately, new rules applied to our sensor started to consume too much CPU
(not too much, but causing host load to go to 0.4 permanent). I folowed
the problem and found it was PCRE causing it. The problem is that this
is causing some TREMENDOUS delays in packets... from 50 to 1000 ms, in
some packets (doing a ping, 1 every 30 or so packets gets delayed).

So, How do yo think "config pcre_match_limit 100" and "config
pcre_match_limit_recursion 100" would affect detection? (as false

Do you have any other sugestion (aside from not using pcre rules :-)) to
get beter PCRE performance?
Are you running in inline mode, or IDS mode?  Are you dropping packets?
Excuse me :-)
Inline mode. Snort (Ok, planning upgrade anyway). No packets get
droped. Just huge delays in some packets. Delay goes off if I put

config pcre_match_limit 25
onfigpcre_match_limit_recursion 25

But I don't think it's a good idea. Is it?


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