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Cisco Bug: CSCun89616 - IOS Does Not Properly Respond to TLS 1.2 Client Hellos

Last Modified

Apr 17, 2019

Products (25)

  • Cisco IOS
  • Cisco ASR 901-6CZ-FS-D Router
  • Cisco ASR 901-6CZ-F-D Router
  • Cisco ASR 901-4C-FT-D Router
  • Cisco ASR 901S-4SG-F-D Router
  • Cisco ME 3600X-24TS-M Switch
  • Cisco ASR 901S-2SG-F-AH Router
  • Cisco ASR 901-6CZ-F-A Router
  • Cisco ASR 901S-2SG-F-D Router
  • Cisco ASR 901-6CZ-FT-A Router
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Known Affected Releases

15.1(4)M6.10 15.3(3)M1.9 15.4(2)S1 15.4(3)S

Description (partial)

When AnyConnect sends a client hello message using TLS 1.2, IOS headends are unable to respond correctly and send a [FIN, ACK], terminating the session. The connection eventually rebuilds using TLS 1.0, but the process takes over 20 seconds to complete. This behavior causes a sizable delay before receiving the login prompt.

Headend: IOS Router
Client: Windows 8, Android OS, iOS
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