[Snort-devel] odd problems with 2.3rc2

Martin Roesch roesch at ...402...
Sun Jan 23 18:36:15 EST 2005


Hi Russell,

I can't answer why the rule is firing without looking into it a lot 
more but I can tell you what's happening with the tagged packets.  If 
Snort is using unified logging, instead of logging the pseudopacket 
generated by stream4 it will instead log the original packets that 
constituted the stream that was used to generate the pseudopacket in 
the first place.  This is so that you can see what was on the wire 
originally instead of getting the pseudopacket which tends to mess up 
analysts who want to know what the original TTL/TOS/etc were.  The 
unified header contains reference info that will let you see which 
trigger packet (the first in the segment queue) the tagged packets are 
associated with.

Hope this clears things up.

BTW, the reference field isn't all that great, because it is just a 
counter of the number of events since startup.  I floated the idea of 
having a "packet serial number" structure that could be used to 
uniquely identify a sensor, instance and event id that would be 
attached to each unified event and associated tagged packets.

      -Marty


On Jan 10, 2005, at 4:13 PM, Russell Fulton wrote:

> On Mon, 2005-01-10 at 17:19 +0100, Dirk Geschke wrote:
>
>>>
>>> I've just installed RC2 and I have observed a couple of problems:
>>>      1. a few rules are triggering when there does not appear to be 
>>> any
>>>         reason.  One rule is triggering often, for no apparent 
>>> reason:
>>
>> maybe you are using the unified output plugin?
>
> I am.
>>  In this case it
>> is possible that the rules fires on a stream4 rebuild packet.
>> This packet is stored in the original parts and only the first
>> one gets the signature message. All further packets are "Tagged
>> Packet"s and are stored in the log facility.
>
> That explains part of the problem (the tagged packets) but not why the
> rules are triggering in the first place.
>
> Thanks, Russell
>
>
>
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-- 
Martin Roesch - Founder/CTO, Sourcefire Inc. - +1-410-290-1616
Sourcefire - Discover.  Determine.  Defend.
roesch at ...402... - http://www.sourcefire.com
Snort: Open Source Network IDS - http://www.snort.org





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