[Snort-devel] Snort packet sequence numbers remain constant

Shankar Narayan keshi8086 at ...2499...
Thu Dec 6 18:55:47 EST 2012

Cool. Thanks!

Tried it out. Makes more sense now. However isn't this a bit non-intuitive?
The alert shows up for the same stream multiple times with no change in
properties. Is there a way to suppress this such that I can be alerted only
when the entire data has been received or transmitted? Like detecting an
EOF in addition to the existing rule to detect EXEs should throw up just a
single alert statement right?

This in turn leads me to another question:
Is there a nice way to extract files from packet capture in snort while its
configured inline? There are many data carving modules out there which
analyse on pcap dumps but I was wondering if it'd be a cool feature to have
within snort as an additional module.


On Thu, Dec 6, 2012 at 10:19 AM, Russ Combs <rcombs at ...402...> wrote:

> Snort logs the packet or packets that triggered the alert, using the
> sequence and ack numbers therein.
> Although your content may match different raw packets, you may actually be
> alerting on the same stream5 reassembled packet.  Try using:
> stream5_global: show_rebuilt_packets
> and / or snort -A cmg to see where you are alerting.  If it still isn't
> clear, send a pcap and conf and we'll take a look.
> Russ
> On Wed, Dec 5, 2012 at 5:30 PM, Shankar Narayan <keshi8086 at ...2499...>wrote:
>> Hi,
>> I am new to snort and I have been playing around with rules to be able to
>> detect exe files coming through the network.
>> One of the things I noticed when I added my rules was that the sequence
>> number that showed up on all the alert logs were the same. The same was the
>> case for ACKs too.
>> This seems odd as for subsequent packets of the exe download I get the
>> alert with the same tcp seq number and ack!
>> How does the sequence number and ACK number thrown out by the alert logs
>> differ from the one inside the tcp header?
>> Any pointers on what's exactly happening?
>> Thanks,
>> - keshi
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*Real Name: Krishnan Shankar Narayan

*"So let it be written, So let it be done!" *
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