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Cisco Bug: CSCul46582 - ASA: Out of order Fin packet leaves connection half closed

Last Modified

Apr 16, 2020

Products (1)

  • Cisco ASA 5500-X Series Firewalls

Known Affected Releases

8.5(1.16) 9.1(3)

Description (partial)

Symptom:
During the session closing ASA receive out of order FIN packets from one host. ASA keeps this connection as half-closed.

Conditions:
ASA receive out of order FIN packet only from one host (in this case from client)
     Server                                                                                      Client

                  --> (SEQ=407)(ACK=1453)(CTL=FIN,ACK)   --> 
                  <-- (SEQ=1454)(ACK=408)(CTL=ACK)        <--                   
                  <-- (SEQ=1453)(ACK=407)(CTL=FIN,ACK)  <--
                  --> (SEQ=408)(ACK=1454)(CTL=ACK)         -->


During the recreation I changed manually the sequence:
       Server                                                                               Client

                 --> (SEQ=407)(ACK=1453)(CTL=FIN,ACK)   --> 
                 <-- (SEQ=1453)(ACK=407)(CTL=FIN,ACK)  <--
                  <-- (SEQ=1454)(ACK=408)(CTL=ACK)        <--            
                  --> (SEQ=408)(ACK=1454)(CTL=ACK)         -->


 Then connection is tear down normally.
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