Vulnerability Discussion
If an account has an empty password, anyone could log on and run commands with the privileges of that account. Accounts with empty passwords should never be used in operational environments.
Check
To verify that null passwords cannot be used, run the following command:
$ sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iH '^\s*permitemptypasswords'
PermitEmptyPasswords no
If "PermitEmptyPasswords" is set to "yes", this is a finding.
If conflicting results are returned, this is a finding.
Fix
Edit the following line in "etc/ssh/sshd_config" to prevent logons with empty passwords.
PermitEmptyPasswords no
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