The SSH public host key files must have mode 0644 or less permissive.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-75843	UBTU-16-030310	SV-90523r2_rule		Medium

Description
If a public host key file is modified by an unauthorized user, the SSH service may be compromised.

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

Details

Check Text ( C-75531r2_chk )
Verify the SSH public host key files have mode "0644" or less permissive. Note: SSH public key files may be found in other directories on the system depending on the installation. The following command will find all SSH public key files on the system: # ls -l /etc/ssh/*.pub -rw-r--r-- 1 root wheel 618 Nov 28 06:43 ssh_host_dsa_key.pub -rw-r--r-- 1 root wheel 347 Nov 28 06:43 ssh_host_key.pub -rw-r--r-- 1 root wheel 238 Nov 28 06:43 ssh_host_rsa_key.pub If any key.pub file has a mode more permissive than "0644", this is a finding.

Check Text ( C-75531r2_chk )

Verify the SSH public host key files have mode "0644" or less permissive.

Note: SSH public key files may be found in other directories on the system depending on the installation.

The following command will find all SSH public key files on the system:

# ls -l /etc/ssh/*.pub

-rw-r--r-- 1 root wheel 618 Nov 28 06:43 ssh_host_dsa_key.pub
-rw-r--r-- 1 root wheel 347 Nov 28 06:43 ssh_host_key.pub
-rw-r--r-- 1 root wheel 238 Nov 28 06:43 ssh_host_rsa_key.pub

If any key.pub file has a mode more permissive than "0644", this is a finding.

Fix Text (F-82473r2_fix)
Note: SSH public key files may be found in other directories on the system depending on the installation. Change the mode of public host key files under "/etc/ssh" to "0644" with the following command: # sudo chmod 0644 /etc/ssh/*key.pub 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