GRUB: Authentication bypass — GLSA 201512-03

GRUB's authentication prompt can be bypassed by entering a sequence of backspace characters.

Affected Packages

sys-boot/grub on all architectures
Affected versions < 2.02_beta2-r8
Unaffected versions >= 2.02_beta2-r8
revision >= 0.97

Background

GNU GRUB is a multiboot boot loader used by most Linux systems.

Description

An integer underflow in GRUB’s username/password authentication code has been discovered.

Impact

An attacker with access to the system console may bypass the username prompt by entering a sequence of backspace characters, allowing them e.g. to get full access to GRUB’s console or to load a customized kernel.

Workaround

There is no known workaround at this time.

Resolution

All GRUB 2.x users should upgrade to the latest version:

 # emerge --sync
 # emerge --ask --oneshot --verbose ">=sys-boot/grub-2.02_beta2-r8"
 

After upgrading, make sure to run the grub2-install command with options appropriate for your system. See the GRUB2 Quick Start guide in the references below for examples. Your system will be vulnerable until this action is performed.

References

Release Date
December 19, 2015

Latest Revision
December 19, 2015: 1

Severity
normal

Exploitable
local

Bugzilla entries