CVE-2026-97876: Bypass of GRUB lockdown restriction in Secure Boot mode via serial command MMIO base address
A local attacker with control over GRUB's configuration can bypass lockdown restrictions when booting with Secure Boot and load an unsigned GRUB module, while GRUB continues to report lockdown is enabled.
The vulnerability is caused by insufficient validation of the MMIO base address passed to the GRUB serial command. GRUB does not validate that the base address corresponds to a UART device, rather than being an arbitrary memory address. This allows an attacker to trick GRUB into writing non-arbitrary data at an attacker-controlled address, including resetting the grubfileverifiers list in a way that disables the subsequent verification of loaded modules.
Affected Software
Event History
Frequently Asked Questions
Who can exploit this issue?
Exploitation requires local access and control over GRUB's configuration. It affects systems booting GRUB with Secure Boot where an attacker can supply the relevant serial-command MMIO base address.
What does successful exploitation allow?
An attacker can bypass GRUB lockdown restrictions and load an unsigned GRUB module while GRUB continues to report that lockdown is enabled. The described technique resets the grub_file_verifiers list, disabling verification of subsequently loaded modules.
What condition makes the serial command dangerous?
GRUB insufficiently validates the MMIO base address passed to its serial command. Instead of requiring the address to correspond to a UART device, it can be treated as an attacker-controlled memory address for writes.