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1.236 RHEL-09-255175

Information

RHEL 9 SSH daemon must prevent remote hosts from connecting to the proxy display.

GROUP ID: V-258011
RULE ID: SV-258011r1045079

When X11 forwarding is enabled, there may be additional exposure to the server and client displays if the sshd proxy display is configured to listen on the wildcard address. 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.

Solution

Configure the SSH daemon to prevent remote hosts from connecting to the proxy display.

Add the following line to "/etc/ssh/sshd_config" or to a file in "/etc/ssh/sshd_config.d", or uncomment the line and set the value to "yes":

X11UseLocalhost yes

The SSH service must be restarted for changes to take effect:

$ sudo systemctl restart sshd.service

See Also

https://workbench.cisecurity.org/benchmarks/22008

Item Details

Category: CONFIGURATION MANAGEMENT

References: 800-53|CM-6b., CAT|II, CCI|CCI-000366, Rule-ID|SV-258011r1045079_rule, STIG-ID|RHEL-09-255175, Vuln-ID|V-258011

Plugin: Unix

Control ID: 0f2b7c8bc56b196a1c92ef2bb8c1362b592dbb840fd6ce9647926659d585fb53