Vulnerability Discussion

Failure to restrict system access to authenticated users negatively impacts Ubuntu operating system security.

Check

Verify that unattended or automatic login via SSH is disabled with the following command:

$ sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iEH '^\s*(permit(.*?)(passwords|environment))'

PermitEmptyPasswords no
PermitUserEnvironment no

If "PermitEmptyPasswords" or "PermitUserEnvironment" keywords are not set to "no", are missing completely, or are commented out, this is a finding.

If conflicting results are returned, this is a finding.

Fix

Configure the Ubuntu operating system to allow the SSH daemon to not allow unattended or automatic login to the system.

Add or edit the following lines in the "/etc/ssh/sshd_config" file:

PermitEmptyPasswords no
PermitUserEnvironment no

Restart the SSH daemon for the changes to take effect:

$ sudo systemctl restart sshd.service