Vulnerability Discussion

If other users have access to modify user-specific SSH configuration files, they may be able to log on to the system as another user.

Check

Verify the SSH daemon performs strict mode checking of home directory configuration files with the following command:

$ sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iH '^\s*strictmodes'

StrictModes yes

If "StrictModes" is set to "no", is missing, or the returned line is commented out, this is a finding.

If conflicting results are returned, this is a finding.

Fix

Configure SSH to perform strict mode checking of home directory configuration files. Uncomment the "StrictModes" keyword in "/etc/ssh/sshd_config" and set the value to "yes":

StrictModes yes

The SSH daemon must be restarted for the changes to take effect. To restart the SSH daemon, run the following command:

$ sudo systemctl restart sshd.service