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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 Security Technical Implementation Guide 2020-05-29

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.
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