CVE-2025-0678: GNU GRUB2 RCE Vulnerability

CVE-2025-0678 Overview

CVE-2025-0678 is an integer overflow vulnerability in GRUB2's squash4 filesystem module that can lead to heap-based out-of-bounds write and arbitrary code execution. When reading data from a squash4 filesystem, GRUB2 uses user-controlled parameters from the filesystem geometry to determine internal buffer sizes. Due to improper integer overflow checks, a maliciously crafted filesystem can cause buffer size calculations to overflow, resulting in a smaller-than-expected memory allocation via grub_malloc(). Subsequently, the direct_read() function performs a heap-based out-of-bounds write during data reading operations. This vulnerability is particularly dangerous as it can be leveraged to corrupt GRUB's internal critical data structures and potentially bypass Secure Boot protections.

Critical Impact

Successful exploitation enables arbitrary code execution at the bootloader level, potentially bypassing Secure Boot protections and establishing persistent, pre-OS control over affected systems.

Affected Products

• GNU GRUB2 (all versions)
• Red Hat Enterprise Linux 7.0, 8.0, and 9.0
• Red Hat OpenShift Container Platform 4.0

Discovery Timeline

• 2025-03-03 - CVE-2025-0678 published to NVD
• 2025-03-25 - Last updated in NVD database

Technical Details for CVE-2025-0678

Vulnerability Analysis

This vulnerability resides in GRUB2's squash4 filesystem driver, which handles the reading of SquashFS compressed filesystems during the boot process. The core issue stems from improper validation of integer arithmetic when calculating buffer sizes based on filesystem geometry parameters.

When GRUB2 mounts a squash4 filesystem, it reads metadata including block sizes and other geometry information. These values are directly used in arithmetic operations to determine how much memory should be allocated for internal buffers. The vulnerability manifests because the code fails to properly validate whether these calculations result in integer overflows.

The CWE-190 (Integer Overflow or Wraparound) classification accurately describes this vulnerability. When filesystem geometry parameters are crafted with specific values, the multiplication or addition operations used to calculate buffer sizes can wrap around, producing a small result instead of the expected large value. The subsequent memory allocation is therefore insufficient for the actual data being read.

Root Cause

The root cause is the absence of proper integer overflow checks in the squash4 filesystem module's buffer size calculations. The code trusts user-controlled filesystem geometry values and uses them directly in arithmetic operations without validating that the results stay within expected bounds. This allows an attacker to craft a malicious filesystem where the geometry parameters cause integer wraparound during buffer size computation.

Attack Vector

Exploitation requires local access with the ability to present a maliciously crafted squash4 filesystem image to GRUB2 during the boot process. An attacker would need to:

1. Create a specially crafted squash4 filesystem with geometry parameters designed to trigger integer overflow
2. Position this filesystem where GRUB2 will attempt to read it during boot (e.g., on a bootable USB drive, network boot image, or by modifying existing boot media)
3. When GRUB2 attempts to read from this filesystem, the integer overflow occurs during buffer allocation
4. The subsequent direct_read() operation writes beyond the allocated heap buffer
5. The heap corruption can be leveraged to overwrite critical GRUB internal structures, potentially achieving arbitrary code execution

The attack is particularly significant because code execution at the bootloader level occurs before the operating system loads, potentially allowing bypass of Secure Boot and other security mechanisms.

Detection Methods for CVE-2025-0678

Indicators of Compromise

• Unexpected or modified squash4 filesystem images present on boot media or network boot infrastructure
• Signs of bootloader tampering or unexpected GRUB2 configuration changes
• System boot failures or crashes during the early boot phase when reading squash4 filesystems
• Secure Boot validation failures where previously trusted systems fail attestation

Detection Strategies

• Implement integrity monitoring for boot media and GRUB2 configurations using cryptographic hashing
• Enable and monitor Secure Boot status and UEFI event logs for signs of bootloader compromise
• Use hardware-based attestation mechanisms (TPM) to detect unauthorized bootloader modifications
• Monitor for unauthorized physical access to systems or boot infrastructure

Monitoring Recommendations

• Regularly verify GRUB2 binary integrity against known-good hashes from your distribution vendor
• Implement boot-time logging and alerting for unexpected filesystem mount operations
• Review network boot infrastructure for unauthorized squash4 filesystem images
• Deploy endpoint protection with pre-boot integrity verification capabilities

How to Mitigate CVE-2025-0678

Immediate Actions Required

• Apply vendor-provided GRUB2 security updates as soon as they become available from your distribution
• Review and restrict physical access to systems, particularly those with Secure Boot requirements
• Audit boot media and network boot infrastructure for unauthorized or unexpected squash4 filesystems
• Consider temporarily disabling boot from removable media on high-security systems until patches are applied

Patch Information

Affected organizations should monitor vendor security advisories for patch availability. Red Hat has acknowledged this vulnerability and tracking information is available through their security portal. For the latest patch status and remediation guidance:

• Red Hat CVE-2025-0678 Advisory
• Red Hat Bug Report #2346118

Organizations using Red Hat Enterprise Linux 7.0, 8.0, 9.0, or OpenShift Container Platform 4.0 should prioritize tracking these advisories for specific package versions containing the fix.

Workarounds

• Restrict boot to trusted, signed boot media only by configuring UEFI/BIOS settings appropriately
• Enable and enforce Secure Boot to help limit the impact of bootloader-level exploits
• Disable network boot (PXE) on systems where it is not required
• Implement physical security controls to prevent unauthorized access to boot media and BIOS settings

# Verify GRUB2 package version on Red Hat-based systems
rpm -qa | grep grub2

# Check current Secure Boot status
mokutil --sb-state

# List installed GRUB2 modules to identify squash4 usage
ls -la /boot/grub2/*/squash4.mod 2>/dev/null || echo "squash4 module not found"