GRUB2 Denial of Service

The GRUB2 bootloader is a widely used software for managing the boot process in Linux systems. The network module within GRUB2 allows it to communicate with the network interface card (NIC). This vulnerability, known as a Use-after-Free issue, occurs because the net_set_vlan command is not properly unregistered when the network module is unloaded from memory. As a result, an attacker can force the system to access memory locations that are no longer valid, leading to system instability and potential crashes.

This vulnerability affects GRUB2 versions 2.04-2.08. The exact version range is not specified in the advisory. To check if you're affected, run the following command: grub --version | grep net on Linux systems or grub --version on macOS.

Note that this vulnerability does not affect GRUB1 or other bootloader software.

To fix this vulnerability, update to a newer version of GRUB2. The latest stable version is 2.10. You can download it from the official Red Hat website: https://www.redhat.com/en/blog/grub-20-released-grub-21-pre-alpha. Alternatively, you can use the following command to upgrade on Linux systems:

sudo grub-install --version | grep net

If an immediate fix isn't possible, consider implementing the following mitigations:

• Restrict network access to your GRUB2 instance (firewall it from the public internet)
• Audit GRUB2 configuration for suspicious settings
• Monitor for signs of instability or crashes

• access.redhat.com
• bugzilla.redhat.com
• www.openwall.com