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Cisco Bug: CSCur69227 - ASA sporadic crypto errors with SSL VPN using TLS1.x DHE ciphers

Last Modified

Apr 16, 2020

Products (1)

  • Cisco ASA 5500-X Series Firewalls

Known Affected Releases

100.12(0.96) 100.12(10.30) 100.12(10.33) 9.3(1.105)

Description (partial)

ASA may sporadically fail an incoming SSL VPN (TLS1.x)  session  when using Ephemeral Diffie-Hellman-based (DHE) cipher suites.
When this happens ASA will display the 402123 (vpn-CRYPTO) sylog , show counters (PKP_ERRORS) and  show ssl errors . If the SSL connection is retried, the session will be successful.

SSL VPN Clientless and AnyConnect sessions using DHE  TLS 1.x cipher suites.

Connection attempt has failed due to server communication errors is being seen with AnyConnect releases with March OpenSSL update excluding Windows to a very specific head-end configuration. The reason for this failure is that the March OpenSSL update removes the RC4 algorithm from all but WIndows platforms and the DHE algorithms do not function properly on certain older ASA versions due to Defect ID: CSCur69227

AnyConnect (non-Windows) releases from March 2016 ASA versions with defect ID: CSCur69227 and DHE algorithm chosen (ssl encryption)
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