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flexresp3: Reset with TTL of 0
From: Jim Hranicky <jfh () ufl edu>
Date: Tue, 26 Oct 2010 14:32:01 -0400

We're currently testing out flexresp3. We have a snort box in IDS mode 
with the following config: 

  eth0   : management interface
  eth1   : reset interface
  eth2   : sniffing interface

  snort: 2.9.0/daq-0.2

From snort.conf: 

  config response: device eth1 attempts 10
  preprocessor stream5_global: max_tcp 8192, memcap 104857600, track_tcp yes, \
                              track_udp no, max_active_responses 10, \
                              min_response_seconds 1

Our rule is like so: 

  alert tcp $HOME_NET any -> [XX.XX.XX.0/24] $HTTP_PORTS 
  (msg:"UFOISC reset test"; classtype:trojan-activity; sid:9000092; 
  resp:reset_XXXX; )

I've tried 'reset_both' and 'reset_dest' . 

Preliminary tests were not seeing the resets reach the test machine that
was tripping the rule. Sniffing on the reset interface, I found that the 
reset attempts were going out, but the TTL is 0 (see attached). 

I've tried compiling with and without --enable-ipv6 but the result is
the same. 

Has anyone else seen this behavior? I've likely missed a step somewhere. 

I'll be glad to supply more info if needed. 

Jim Hranicky
IT Security Engineer
Office of Information Security and Compliance
University of Florida

Attachment: rst.txt

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