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Cisco Bug: CSCuq80704 - ASA classifies TCP packets as PAWS failure incorrectly

Last Modified

Sep 13, 2019

Products (1)

  • Cisco ASA 5500-X Series Firewalls

Known Affected Releases

9.1(5) 9.4(3) 9.4(3.4) 9.6(1)

Description (partial) 

Symptom:
The ASA may incorrectly classify some TCP segments as failing a PAWS test when the TS.value present in the tcp header wraps around the 2^32 mark. Per RFC 1323, this should not cause the connect to fail. When a packet hits the ASA on an existing connection, the packet is dropped and the counter below increments:

ciscoasa/pri/act# sh asp drop

Frame drop:
 TCP packet failed PAWS test (tcp-paws-fail)

Conditions:
This occurs when the TS.value in a TCP packet/connection wraps around the 2^32 limit for that counter.
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