The SSH private host key files must have mode 0600 or less permissive.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-75845	UBTU-16-030320	SV-90525r2_rule		Medium

Description
If an unauthorized user obtains the private SSH host key file, the host could be impersonated.

STIG	Date
Canonical Ubuntu 16.04 LTS Security Technical Implementation Guide	2018-07-18

Details

Check Text ( C-75533r2_chk )
Verify the SSH private host key files have mode "0600" or less permissive. Check the mode of the private host key files under "/etc/ssh" file with the following command: # ls -alL /etc/ssh/ssh_host*key -rw------- 1 root wheel 668 Nov 28 06:43 ssh_host_dsa_key -rw------- 1 root wheel 582 Nov 28 06:43 ssh_host_key -rw------- 1 root wheel 887 Nov 28 06:43 ssh_host_rsa_key If any private host key file has a mode more permissive than "0600", this is a finding.

Check Text ( C-75533r2_chk )

Verify the SSH private host key files have mode "0600" or less permissive.

Check the mode of the private host key files under "/etc/ssh" file with the following command:

# ls -alL /etc/ssh/ssh_host*key

-rw------- 1 root wheel 668 Nov 28 06:43 ssh_host_dsa_key
-rw------- 1 root wheel 582 Nov 28 06:43 ssh_host_key
-rw------- 1 root wheel 887 Nov 28 06:43 ssh_host_rsa_key

If any private host key file has a mode more permissive than "0600", this is a finding.

Fix Text (F-82475r2_fix)
Configure the mode of SSH private host key files under "/etc/ssh" to "0600" with the following command: #sudo chmod 0600 /etc/ssh/ssh_host*key 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