Secure Shell (SSH) 2 in Cisco IOS 12.0 through 12.3 allows remote attackers to cause a denial of service (device reload) (1) via a username that contains a domain name when using a TACACS+ server to authenticate, (2) when a new SSH session is in the login phase and a currently logged in user issues a send command, or (3) when IOS is logging messages and an SSH session is terminated while the server is sending data.
Secure Shell (SSH) 2 in Cisco IOS 12.0 through 12.3 allows remote attackers to cause a denial of service (device reload) (1) via a username that contains a domain name when using a TACACS+ server to authenticate, (2) when a new SSH session is in the login phase and a currently logged in user issues a send command, or (3) when IOS is logging messages and an SSH session is terminated while the server is sending data.
Cisco devices running Cisco Internetworking Operating System Software (IOS) are vulnerable to a denial of service attack. If the IOS device has been configured as an SSH (Secure Shell) version 2 server, and the logging of messages is directed to an established SSH session (using the terminal monitor command), while the SSH session to the device terminates when the SSH server is sending data to the client, the attacker could cause the device to reload. An attacker could repeat exploitation of this vulnerability to cause a sustained denial of service.
Note: It is reported that this vulnerability only effects SSH protocol version 2.