CVE-2025-1125: GNU GRUB2 HFS Filesystem RCE Vulnerability

CVE-2025-1125 Overview

CVE-2025-1125 is an integer overflow vulnerability in GNU GRUB2's HFS filesystem module that can lead to arbitrary code execution and secure boot bypass. When reading data from an HFS filesystem, the module uses user-controlled parameters from filesystem metadata to calculate internal buffer sizes without properly validating for integer overflow conditions. A maliciously crafted filesystem can cause buffer size calculations to overflow, resulting in undersized memory allocations. The hfsplus_open_compressed_real() function subsequently writes past the allocated buffer length, corrupting GRUB's internal critical data structures.

Critical Impact

This vulnerability enables attackers with local access to bypass secure boot protections through arbitrary code execution in the bootloader context, potentially compromising the entire system trust chain.

Affected Products

• GNU GRUB2 (all versions prior to patch)

Discovery Timeline

• 2025-03-03 - CVE-2025-1125 published to NVD
• 2026-01-08 - Last updated in NVD database

Technical Details for CVE-2025-1125

Vulnerability Analysis

This vulnerability resides in GRUB2's HFS filesystem handling code, specifically within the compressed file handling functionality. The HFS module processes filesystem metadata parameters to determine buffer sizes for internal operations. However, the code fails to implement proper integer overflow checks when performing arithmetic operations on these user-controlled values.

When processing a specially crafted HFS filesystem image, the buffer size calculations can wrap around due to integer overflow, causing grub_malloc() to allocate a significantly smaller buffer than intended. The hfsplus_open_compressed_real() function then operates on this undersized buffer, writing beyond its boundaries. This out-of-bounds write condition (CWE-787) allows attackers to corrupt adjacent memory regions containing GRUB's critical internal data structures.

The exploitation requires local access and user interaction, typically involving mounting a malicious filesystem image during the boot process. Successful exploitation can bypass secure boot protections, as the malicious code executes within GRUB's trusted execution context before the operating system loads.

Root Cause

The root cause is missing integer overflow validation in buffer size calculations within the HFS filesystem module. When filesystem metadata contains carefully chosen values, the multiplication or addition operations used to compute buffer sizes overflow, producing a small positive value. The subsequent memory allocation succeeds but creates an insufficient buffer, and the code proceeds to write data assuming the full calculated size is available.

Attack Vector

The attack requires local access to the target system and involves presenting a maliciously crafted HFS filesystem image to GRUB2 during the boot process. An attacker could accomplish this by:

1. Creating a specially crafted HFS filesystem image with malicious metadata values designed to trigger the integer overflow
2. Placing this image on a bootable medium or accessible storage device
3. Causing the target system to boot from or access this malicious filesystem
4. The overflow leads to heap corruption within GRUB, enabling arbitrary code execution in the bootloader context

The vulnerability exploits the trust boundary between filesystem metadata and the bootloader's memory management, allowing the attacker to execute code before secure boot verification completes.

Detection Methods for CVE-2025-1125

Indicators of Compromise

• Unexpected HFS filesystem images present on boot media or accessible storage devices
• Unusual boot failures or system crashes during the GRUB2 boot phase
• Modified or corrupted GRUB2 installation files or configuration
• Evidence of tampering with EFI System Partition contents
• Unexpected changes to secure boot configuration or signing keys

Detection Strategies

• Monitor for unexpected HFS filesystem mounts or access attempts during boot sequences
• Implement file integrity monitoring on bootloader components and EFI partitions
• Enable secure boot logging and review logs for verification failures or anomalies
• Deploy endpoint detection solutions capable of monitoring pre-OS boot activities
• Audit removable media policies to prevent unauthorized bootable devices

Monitoring Recommendations

• Enable UEFI audit logging to capture boot-time security events
• Implement continuous monitoring of EFI System Partition integrity
• Configure alerts for any modifications to GRUB2 binaries or modules
• Monitor for unusual storage device access patterns during system startup

How to Mitigate CVE-2025-1125

Immediate Actions Required

• Update GRUB2 to the latest patched version provided by your distribution vendor
• Verify secure boot is enabled and properly configured on affected systems
• Review and restrict access to boot media and EFI partitions
• Audit systems for signs of compromise before applying patches
• Consider disabling HFS filesystem support in GRUB2 if not required

Patch Information

GNU GRUB2 developers have addressed this vulnerability in a security update. Users should apply patches through their Linux distribution's package management system. For detailed patch information and updated packages, consult the GNU GRUB Development Update. Red Hat users can find distribution-specific guidance in the Red Hat CVE Advisory and track resolution progress via the Red Hat Bug Report.

Workarounds

• Disable HFS filesystem support in GRUB2 by removing or blacklisting the hfs and hfsplus modules
• Restrict physical access to systems to prevent boot from malicious media
• Implement strict removable media policies to control bootable device access
• Use platform firmware settings to limit boot device options
• Enable TPM-based measured boot to detect bootloader tampering

# Remove HFS module from GRUB installation (if not needed)
# Location may vary by distribution
sudo rm /boot/grub/i386-pc/hfs.mod 2>/dev/null
sudo rm /boot/grub/i386-pc/hfsplus.mod 2>/dev/null
sudo rm /boot/grub/x86_64-efi/hfs.mod 2>/dev/null
sudo rm /boot/grub/x86_64-efi/hfsplus.mod 2>/dev/null

# Regenerate GRUB configuration without HFS support
sudo grub-mkconfig -o /boot/grub/grub.cfg