[Oisf-devel] UDP rule triggering on wrong port

Chris Wakelin c.d.wakelin at reading.ac.uk
Wed Mar 30 13:54:03 UTC 2011

On 08/02/11 18:13, Chris Wakelin wrote:
>>> (I've also got a UDP rule occasionally triggering on the wrong port;
>>> I'll see if I can get a packet dump for that.)
>> I'd love to get more details on this.
>> Cheers,
>> Victor
> Hmm, interestingly I haven't seen the UDP problem (on the Srzibi
> emerging-trojans rule; destination port should be 1024 but it was
> hitting randomly) since I updated yesterday, either.

Actually it was because emerging-trojan.rules dropped out of my
suricata.yaml :(. I think it's missing in the latest git master sample too.

Anyway, I've got a packet capture to reproduce it (attached). It's
hitting the rule:

> alert udp $HOME_NET any -> $EXTERNAL_NET 1024: (msg:"ET TROJAN Srizbi registering with controller"; dsize:20; content:"|2d|"; offset:6; content:"|2d|"; distance:6; within:1; content:!"|00|server."; offset:44; classtype:trojan-activity; reference:url,www.secureworks.com/research/threats/ronpaul/; reference:url,doc.emergingthreats.net/2007711; reference:url,www.emergingthreats.net/cgi-bin/cvsweb.cgi/sigs/VIRUS/TROJAN_Srizbi; sid:2007711; rev:9;)

which should only match on destination port 1024.

The traffic was probably peer-to-peer filesharing of some kind ...

Best Wishes,

Christopher Wakelin,                           c.d.wakelin at reading.ac.uk
IT Services Centre, The University of Reading,  Tel: +44 (0)118 378 8439
Whiteknights, Reading, RG6 6AF, UK              Fax: +44 (0)118 975 3094
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