A certain Debian patch for GNU GRUB uses world-readable permissions for grub.cfg, which allows local users to obtain password hashes, as demonstrated by reading the password_pbkdf2 directive in the file.
GNU GRand Unified Bootloader (GRUB) 2 1.97 only compares the submitted portion of a password with the actual password, which makes it easier for physically proximate attackers to conduct brute force attacks and bypass authentication by submitting a password whose length is 1.