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:

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

set superusers="<accountname>"
export superusers
password_pbkdf2 <accountname> ${GRUB2_PASSWORD}

Verify <accountname> is not a common name such as root, admin, or administrator.

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

Fix

Configure RHEL 9 to have a unique username for the grub superuser account.

Edit the "/etc/grub.d/01_users" file and add or modify the following lines with a nondefault username for the superuser account:

set superusers="<accountname>"
export superusers

Once the superuser account has been added, update the grub.cfg file by running:

Regenerate the GRUB configuration:
$ sudo grub2-mkconfig -o /boot/grub2/grub.cfg

Reboot the system:
$ sudo reboot