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The SUSE operating system SSH daemon must prevent remote hosts from connecting to the proxy display.


Overview

Finding ID Version Rule ID IA Controls Severity
V-233308 SLES-12-030261 SV-233308r603331_rule Medium
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 DIPSLAY environment variable to localhost. This prevents remote hosts from connecting to the proxy display.
STIG Date
SLES 12 Security Technical Implementation Guide 2023-06-02

Details

Check Text ( C-36503r622236_chk )
Verify the SUSE operating system SSH daemon prevents remote hosts from connecting to the proxy display.

Check the SSH X11UseLocalhost setting with the following command:

# sudo grep -i x11uselocalhost /etc/ssh/sshd_config
X11UseLocalhost yes

If the "X11UseLocalhost" keyword is set to "no", is missing, or is commented out, this is a finding.
Fix Text (F-36467r622237_fix)
Configure the SUSE operating system SSH daemon to prevent remote hosts from connecting to the proxy display.

Edit the "/etc/ssh/sshd_config" file to uncomment or add the line for the "X11UseLocalhost" keyword and set its value to "yes" (this file may be named differently or be in a different location if using a version of SSH that is provided by a third-party vendor):

X11UseLocalhost yes