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Cisco Bug: CSCup76212 - ASA rewrites incorrect content-length in SIP message

Last Modified

Nov 27, 2020

Products (1)

  • Cisco Adaptive Security Appliance (ASA) Software

Known Affected Releases

8.4(7.20) 9.0(4.13) 9.1(5.7)

Description (partial)

A SIP receiver endpoint intermittently fails to parse a SIP message (e.g. INVITE) because of extra characters in the beginning of message, causing call failures
A SIP receiver endpoint receives Malformed SIP message.

- SIP inspection is enabled on ASA.
- A SIP message sent by the sender contains a SIP payload. For example, XML dialog-info in NOTIFY packet. This message doesn't have to be the same message that was rejected by receiver. Any message sent previously in same connection can trigger the problem.
- That SIP payload (the XML portion, and not the message itself), contains a SIP URI. For example, sip:12345@X.X.X.X:5060. 
- The ASA is to rewrite the SIP URI using a PAT (Port Address Translation) rule.
- The port that ASA chooses for Port Address Translation (PAT) of URI, is different from the original port in the URI.
Note: Sometimes, the URI doesn't contain any port. It is assumed to be 5060 in those cases.
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