CVE-2025-61662: GNU GRUB2 Use-After-Free Vulnerability

CVE-2025-61662 Overview

CVE-2025-61662 is a Use-After-Free vulnerability [CWE-416] in the GNU GRUB bootloader's gettext module. The flaw exists because the gettext command remains registered in memory after its parent module is unloaded. A local attacker with access to the GRUB command environment can invoke the orphaned command, forcing GRUB to dereference memory that is no longer valid. The primary outcome is a crash of the bootloader, producing a Denial of Service. The vendor advisory also notes that data integrity and confidentiality compromise cannot be ruled out, given that GRUB executes in a pre-boot context with full platform privileges.

Critical Impact
A local authenticated attacker can trigger a use-after-free in GRUB's gettext command, crashing the bootloader and potentially undermining pre-boot integrity guarantees such as Secure Boot chain-of-trust assumptions.

Affected Products

GNU GRUB2 (upstream)
Red Hat Enterprise Linux distributions shipping grub2 (see referenced RHSAs)
Downstream Linux distributions repackaging GRUB2

Discovery Timeline

2025-11-18 - CVE-2025-61662 published to NVD
2025-11-18 - Coordinated disclosure via OpenWall oss-security mailing list and GNU GRUB development list
2026-06-30 - Last updated in NVD database

Technical Details for CVE-2025-61662

Vulnerability Analysis

GRUB uses a modular architecture in which optional functionality is provided by loadable modules. Each module registers commands into a global command table when loaded and is expected to unregister them when unloaded. The gettext module, which provides internationalization support for GRUB messages, fails to fully deregister the gettext command during module teardown.

As a result, the command entry in GRUB's dispatch table continues to reference function pointers and data structures that belonged to the unloaded module. Invoking gettext after rmmod gettext causes GRUB to jump into or dereference memory that has been freed or repurposed. The outcome is undefined behavior, typically a crash of the bootloader before the operating system kernel is loaded.

Root Cause

The root cause is incomplete cleanup logic in the gettext module's finalization path. When the module is unloaded, associated command handlers are not removed from GRUB's global command registry. This creates a dangling reference: the command dispatcher still has a valid entry, but the code and data backing that entry have been released. This pattern is a classic Use-After-Free [CWE-416] condition.

Attack Vector

Exploitation requires local access to the GRUB command line or to a GRUB configuration path that permits arbitrary command execution. An attacker with such access loads and unloads the gettext module, then invokes the now-orphaned command. Because GRUB runs before the operating system, successful exploitation can disrupt boot, defeat availability of the platform, and potentially interfere with measured or verified boot mechanisms.

No public proof-of-concept exploit code is available. The vulnerability mechanism is described in the GNU GRUB development mailing list post and Red Hat's advisory tracking; refer to the GNU GRUB Development Mailing List Post and the Red Hat CVE Report CVE-2025-61662 for technical detail.

Detection Methods for CVE-2025-61662

Indicators of Compromise

Unexpected boot failures, kernel panics before OS handoff, or repeated GRUB rescue-shell prompts on affected systems.
Modifications to /boot/grub2/grub.cfg or /etc/grub.d/ scripts that introduce insmod gettext followed by rmmod gettext sequences.
Presence of unauthorized entries invoking the gettext command in custom GRUB menu entries.

Detection Strategies

Inventory installed grub2 package versions across the fleet and compare against fixed versions listed in the referenced Red Hat Security Advisories.
Monitor filesystem integrity for /boot contents, GRUB configuration files, and GRUB module directories (/boot/grub2/i386-pc/, /boot/grub2/x86_64-efi/).
Correlate unexplained reboot loops or boot-time failures with recent changes to bootloader configuration.

Monitoring Recommendations

Enable and review audit rules covering /boot, /etc/default/grub, and /etc/grub.d/ for unauthorized modification.
Alert on privileged shell activity that runs grub2-mkconfig, grub2-install, or edits GRUB module files outside sanctioned patch windows.
Track Secure Boot and measured-boot attestation events for anomalies indicating pre-OS tampering.

How to Mitigate CVE-2025-61662

Immediate Actions Required

Apply vendor-supplied grub2 updates as soon as they are available for your distribution. Red Hat customers should install the applicable errata from the Red Hat CVE Report CVE-2025-61662.
Restrict physical and remote console access to systems where interactive GRUB command-line use is possible.
Enforce a GRUB password on the command line and edit functions using grub2-mkpasswd-pbkdf2 and the password_pbkdf2 directive.

Patch Information

Red Hat has issued a large set of advisories addressing CVE-2025-61662 across its product lines, including RHSA-2026:4648, RHSA-2026:4649, RHSA-2026:4652, RHSA-2026:4653, RHSA-2026:4654, RHSA-2026:4760, RHSA-2026:4822, RHSA-2026:10097, and additional errata through RHSA-2026:17596. Upstream fixes are tracked on the GNU GRUB Development Mailing List.

Workarounds

Disable interactive editing of GRUB menu entries by setting a superuser password and marking entries with --unrestricted only where required.
Remove or avoid loading the gettext module in constrained boot environments where internationalized messages are not needed.
Enforce Secure Boot and validate that only signed, vendor-supplied GRUB binaries execute on the platform.

bash

# Configuration example: enforce GRUB superuser and password
# 1) Generate a PBKDF2 hash
grub2-mkpasswd-pbkdf2

# 2) Add the following to /etc/grub.d/40_custom
set superusers="admin"
password_pbkdf2 admin grub.pbkdf2.sha512.10000.<HASH>

# 3) Regenerate the GRUB configuration
grub2-mkconfig -o /boot/grub2/grub.cfg     # BIOS systems
grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg   # UEFI systems