Title

The sshd server must bind the X11 forwarding server to the loopback address. (Cat II impact)

Discussion

Enabling X11 Forwarding on the host can permit a malicious user to secretly open another X11 connection to another remote client during the session and perform unobtrusive activities such as keystroke monitoring. If the X11 services are not required for the system's intended function, they should be disabled or restricted as appropriate to the user's needs. By default, sshd binds the forwarding server to the loopback address and sets the hostname part of the DISPLAY environment variable to “localhost”. This prevents remote hosts from connecting to the proxy display.

Check Content

Determine if the X11 forwarding server is bound to the loopback address. # grep "^X11UseLocalhost" /etc/ssh/sshd_config If the output of this command is not “X11UseLocalhost yes”, this is a finding.

Fix Text

The root role is required. Modify the sshd_config file. # vi /etc/ssh/sshd_config Locate the line containing: X11UseLocalhost Change it to: X11UseLocalhost yes Restart the SSH service. # svcadm restart svc:/network/ssh

Additional Identifiers

Rule ID: SV-233305r603295_rule

Vulnerability ID: V-233305

Group Title: SRG-OS-000480

Expert Comments

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