Vulnerability Discussion

Having a nondefault grub superuser username makes password-guessing attacks less effective.

Check

Verify the boot loader superuser account has been set with the following command:

$ grep -A1 "superusers" /etc/grub2.cfg

set superusers="superman"
export superusers
password_pbkdf2 superman ${GRUB2_PASSWORD}

In this example "superman" is the actual account name, changed from the default "root".

If superusers contains easily guessable usernames, this is a finding.

Fix

Configure AlmaLinux OS 9 to have a unique username for the grub superuser account using the following commands:

$ sed -ri 's/root/superman/' /etc/grub.d/01_users

$ grub2-mkconfig -o /boot/grub2/grub.cfg