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="<superusers-account>"
export superusers

The <superusers-account> is the actual account name different from common names like 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 in the "### BEGIN /etc/grub.d/01_users ###" section:

set superusers="superusers-account"
export superusers

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

$ sudo grubby --update-kernel=ALL