The Authentication Proxy feature in Cisco IOS does not properly handle invalid AAA return codes from RADIUS and TACACS+ servers, which allo…

The Authentication Proxy feature in Cisco IOS does not properly handle invalid AAA return codes from RADIUS and TACACS+ servers, which allows remote attackers to bypass authentication in opportunistic circumstances via a connection attempt that triggers an invalid code, as demonstrated by a connection attempt with a blank password, aka Bug IDs CSCuo09400 and CSCun16016.