AlmaLinux OS 9 SSH daemon must disable remote X connections for interactive users.

An XCCDF Rule

Description

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.

ID: SV-269270r1050152_rule
Version: ALMA-09-021470
Severity: Medium
References: CCI-000366
Updated: about 2 months ago

Remediation Templates

Configure the SSH daemon to not allow X11 forwarding.

Add the following line to "/etc/ssh/sshd_config", or uncomment the line and set the value to "no":

X11forwarding no
Alternatively, add the setting to an include file if the line "Include /etc/ssh/sshd_config.d/*.conf" is found at the top of the "/etc/ssh/sshd_config" file:

$ echo 'X11forwarding no' > /etc/ssh/sshd_config.d/40-x11forwarding.conf

Restart the SSH daemon for the settings to take effect:

$ systemctl restart sshd.service

AlmaLinux OS 9 SSH daemon must disable remote X connections for interactive users.

Description

Remediation Templates

A Manual Procedure