OpenSSH X11UseLocalhost X11 Forwarding Port Hijacking
Low Nessus Plugin ID 44080
SynopsisThe remote SSH service may be affected by an X11 forwarding port hijacking vulnerability.
DescriptionAccording to its banner, the version of SSH installed on the remote host is older than 5.1 and may allow a local user to hijack the X11 forwarding port. The application improperly sets the 'SO_REUSEADDR' socket option when the 'X11UseLocalhost' configuration option is disabled.
Note that most operating systems, when attempting to bind to a port that has previously been bound with the 'SO_REUSEADDR' option, will check that either the effective user-id matches the previous bind (common BSD-derived systems) or that the bind addresses do not overlap (Linux and Solaris). This is not the case with other operating systems such as HP-UX.
SolutionUpgrade to OpenSSH version 5.1 or later.