Re: lots of false positives for "GPL SQL user name buffer overflow attempt"

["Joel Esler (jesler)" <jesler () cisco com>]

isdataat reads a whole stream, so if packets are being reassembled as part of the Stream5 preprocessor, isdataat can 
cross those packet boundaries, while you may only receive one packet in the alert.


That may be the cause of it.  It doesn’t look that rule matches the rule in the official ruleset, yet another reason 
why ET forking these rules was a bad idea.


On Jan 21, 2014, at 8:48 AM, Cyrille Bollu <cyrille.bollu () gmail com<mailto:cyrille.bollu () gmail com>> wrote:

Hi,

Signature 2102650 generates lots of false positives here.

alert tcp $EXTERNAL_NET any -> $SQL_SERVERS $ORACLE_PORTS (msg:"GPL SQL user name buffer overflow attempt"; 
flow:to_server,established; content:"connect_data"; nocase; content:"|28|user="; nocase; isdataat:1000,relative; 
content:!"|22|"; within:1000; 
reference:url,www.appsecinc.com/Policy/PolicyCheck62.html<http://www.appsecinc.com/Policy/PolicyCheck62.html>; 
classtype:attempted-user; sid:2102650; rev:3;)

It seems like the "isdataat:1000,relative" option is not taken into account, as packets are smaller than 1000 bytes.

For example, here are the last bytes of a matching packet: "(HOST=PC-MARIANNE)(USER=marianne))))".

I can provide you with a packet capture if you want

Br,

Cyrille







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