Vulnerability Discussion

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

Check

Verify that OL 9 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 the "StrictModes" keyword is set to "no", the returned line is commented out, or no output is returned, this is a finding.

Fix

Configure the SSH daemon to perform strict mode checking of home directory configuration files.

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":

StrictModes yes

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

$ sudo systemctl restart sshd.service