The SSH daemon must perform strict mode checking of home directory configuration files.

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

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

$ sshd -T | grep strictmodes

strictmodes yes

If the "StrictModes" keyword is set to "no", or no output is returned, this is a finding.

To configure the SSH daemon to perform strict mode checking of home directory configuration files, add or modify the following line in "/etc/ssh/sshd_config", or uncomment the line and set the value to "yes":

StrictModes yes

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 "StrictModes yes" > /etc/ssh/sshd_config.d/strictmodes.conf

Restart the SSH daemon for the settings to take effect:

$ systemctl restart sshd.service