[Snort-sigs] sid:13272; rule is not so good

Joel Esler jesler at ...435...
Tue Dec 6 15:44:10 EST 2011


That rule is now at rev 5.  There have been modifications to it to improve performance.

J

On Dec 6, 2011, at 2:46 PM, Miso Patel wrote:

> My engineers say rule sid:13272; is not performing good.  Here is it:
> 
> misc.rules:alert tcp $EXTERNAL_NET $HTTP_PORTS -> $HOME_NET any
> (msg:"MISC Microsoft Windows ShellExecute and IE7 mailto url handling
> code execution attempt"; flow:to_client,established;
> content:"mailto|3A|";
> pcre:"/[^\n]*?[\x25\x22]\x2E(com|bat|cmd|exe)/Ri"; metadata:policy
> security-ips drop, service http; reference:bugtraq,25945;
> reference:cve,2007-3896;
> reference:url,www.microsoft.com/technet/security/advisory/943521.mspx;
> reference:url,www.microsoft.com/technet/security/bulletin/ms07-057.mspx;
> classtype:attempted-user; sid:13272; rev:3;)
> 
> They say it is just a 'mailto:' match (which seems common with the web
> pages these days) and then a "Regular Expression" which is causing our
> sensors to not like it and CPU is consumed.
> 
> I know we run a slightly older rules (due to antiquated hardware,
> corporate bureaucratic red tape, etc.) but are all these rules so bad?
> My engineers say this is not good and I wonder if we are detecting on
> what we need to or if there are dropped packets due to so much bad
> rules using CPU and RAM?  Is there a better rule list I can use for my
> sensors?
> 
> Thank you.
> 
> Miso, CISO
> 
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