RE: Fast [SYN], [FIN, ACK] to port 80 with no data

["Hartman, Shane" <SHARTMAN () thezenith com>]

It looks like you have the information you need, you have a no payload
packet with flags set. You just need to write a rule to detect that setup if
there isn't already one in place. The only way to drop the packets is to
turn on active response.

-----Original Message-----
From: snort-users-admin () lists sourceforge net
[mailto:snort-users-admin () lists sourceforge net] On Behalf Of Marc Cozzi
Sent: Tuesday, January 10, 2006 9:24 AM
To: snort-users () lists sourceforge net
Subject: [Snort-users] Fast [SYN], [FIN, ACK] to port 80 with no data



I am observing IP hosts on a network here that are opening connections
[SYN], to port 80(http) on remote systems then immediately closing [FIN,ACK]
the connection or usually within about 90ms. Then again within a min or so,
repeat. It also seems there is zero data exchanged between the connected
systems. I'm guessing it is a status polling application that is determining
if a remote system is up or down.
Probably not a necessary activity on the network and possibly interpreted by
remote network managers as scans/probes/mapping attempts.

Question is:
Is there a way to detect, within snort, this rapid opening and closing of
remote port 80 and fire off an alert. Also, maybe fire off a block of the
remote system?

Thanks for any ideas.


  --marc



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