OpenSSH X11 < 5.1 Session Hijacking

According to its banner, the version of SSH installed on the remote host is older than 5.1. Such versions may allow a local user to hijack X11 sessions because it improperly checks user privileges before re-binding a port. In order for the attack to be successful, the ‘X11UseLocalhost’ option would need to be disabled. By default, the option is enabled. Further, the OpenSSH service would need to be running on an operating system (such as HP-UX) where the effective user ID is not checked.

Note: NNM has solely relied on the banner of the SSH client to perform this check. Any backported patches or workarounds such as recompiling or edited configurations are not observable through the banner.