CVE-2025-0622: GRUB2 Use-After-Free Vulnerability

CVE-2025-0622 Overview

A use-after-free vulnerability has been identified in GRUB2's command/gpg module that affects the hook management system during module unloading operations. The flaw occurs when hooks created by loaded modules are not properly removed when the associated module is unloaded. This memory corruption vulnerability allows an attacker to force GRUB2 to invoke hooks that reference freed memory, potentially leading to arbitrary code execution and secure boot bypass.

Critical Impact

This vulnerability could allow attackers to execute arbitrary code during the boot process and bypass secure boot protections, compromising the entire system's chain of trust from the earliest stages of startup.

Affected Products

• GRUB2 bootloader (versions with vulnerable GPG command module)
• Linux distributions using affected GRUB2 versions
• Systems relying on Secure Boot with vulnerable GRUB2 implementations

Discovery Timeline

• 2025-02-18 - CVE-2025-0622 published to NVD
• 2025-09-18 - Last updated in NVD database

Technical Details for CVE-2025-0622

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption flaw that occurs when a program continues to use a memory location after it has been freed. In GRUB2's GPG command module implementation, hooks registered by dynamically loaded modules persist in memory even after the module that created them has been unloaded and its memory deallocated.

The local attack vector requires elevated privileges to exploit but does not require user interaction. When successfully exploited, the vulnerability can compromise the confidentiality, integrity, and availability of the affected system. The potential to bypass secure boot protections makes this vulnerability particularly concerning for enterprise environments that rely on hardware-backed security chains.

Root Cause

The root cause lies in improper lifecycle management of hook registrations within GRUB2's module system. When a module registers hooks during initialization, the hook references are stored in GRUB2's internal data structures. However, when the module is subsequently unloaded, the cleanup routine fails to deregister these hooks. This leaves dangling pointers in the hook table that reference freed memory from the unloaded module.

When GRUB2 later iterates through the hook table and attempts to invoke these stale hooks, it dereferences freed memory, creating a use-after-free condition. An attacker who can control the contents of the freed memory region could redirect execution flow to arbitrary code.

Attack Vector

The attack requires local access to the system with high privileges to manipulate GRUB2 module loading behavior. An attacker would need to:

1. Load a malicious or specifically crafted module that registers hooks
2. Unload the module while keeping its hooks registered
3. Manipulate heap memory to place controlled data at the freed memory location
4. Trigger GRUB2 to invoke the dangling hook, redirecting execution to attacker-controlled code

If successfully exploited during the boot process, the attacker could execute code before the operating system loads, bypassing secure boot protections and potentially establishing persistent, pre-OS-level compromise. Since this occurs before the OS security stack is initialized, traditional endpoint security solutions would not detect the malicious activity.

Detection Methods for CVE-2025-0622

Indicators of Compromise

• Unexpected GRUB2 module loading/unloading activity in boot logs
• Modified or unsigned GRUB2 binaries or modules
• Anomalous boot timing or failures during secure boot validation
• Changes to GRUB2 configuration files (/boot/grub2/grub.cfg or similar)

Detection Strategies

• Monitor boot log integrity for signs of abnormal module operations
• Implement Trusted Platform Module (TPM) measurements to detect boot chain modifications
• Verify GRUB2 binary signatures against known-good hashes
• Enable and monitor UEFI Secure Boot violation logs

Monitoring Recommendations

• Configure system logging to capture boot-time events including GRUB2 module operations
• Implement file integrity monitoring on /boot partition and GRUB2-related files
• Review TPM attestation logs regularly for unexpected boot measurements
• Monitor for unauthorized changes to EFI system partition contents

How to Mitigate CVE-2025-0622

Immediate Actions Required

• Apply vendor-provided patches from Red Hat or your Linux distribution immediately
• Verify Secure Boot is enabled and functioning correctly on affected systems
• Audit GRUB2 configurations for unnecessary or suspicious module loading
• Restrict physical and privileged access to systems pending patching

Patch Information

Red Hat has released security advisories addressing this vulnerability. Administrators should consult the following resources for patching guidance:

• Red Hat Security Advisory RHSA-2025:16154
• Red Hat Security Advisory RHSA-2025:6990
• Red Hat CVE Information for CVE-2025-0622

Additional technical details can be found at Red Hat Bugzilla Bug #2345865.

Organizations should update to the patched GRUB2 versions provided by their distribution and regenerate GRUB2 configurations after applying updates.

Workarounds

• Minimize the number of GRUB2 modules loaded during boot by removing unnecessary module configurations
• Implement strict access controls limiting who can modify GRUB2 configurations and boot partition contents
• Enable UEFI Secure Boot with properly enrolled keys to add defense-in-depth against unsigned bootloader modifications
• Consider implementing measured boot with TPM attestation to detect boot-time compromises

After applying patches, ensure GRUB2 configurations are regenerated using distribution-appropriate commands:

# Regenerate GRUB2 configuration (RHEL/CentOS/Fedora)
grub2-mkconfig -o /boot/grub2/grub.cfg

# Verify GRUB2 package version includes the security fix
rpm -qa | grep grub2

# Check Secure Boot status
mokutil --sb-state