STIGQter: STIG Summary: Canonical Ubuntu 20.04 LTS Security Technical Implementation Guide Version: 1 Release: 1 Benchmark Date: 10 Mar 2021:

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

DISA Rule

SV-238220r653835_rule

Vulnerability Number

V-238220

Group Title

SRG-OS-000480-GPOS-00227

Rule Version

UBTU-20-010049

Severity

CAT II

CCI(s)

• CCI-000366 - The organization implements the security configuration settings.

Weight

10

Fix Recommendation

Configure the 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

Restart the SSH daemon for the changes to take effect:

$ sudo systemctl restart sshd.service

Check Contents

Verify the 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.

Vulnerability Number

V-238220

Documentable

False

Rule Version

UBTU-20-010049

Severity Override Guidance

Verify the 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.

Check Content Reference

M

Target Key

5318

Comments