CVE-2025-0677 Overview
A heap-based buffer overflow vulnerability has been discovered in GRUB2's UFS (Unix File System) module. The flaw exists in the symlink lookup functionality, where the module fails to properly validate the inode's data size before allocating memory to read file content. When the symlink data size overflows, grub_malloc() is called with an insufficient buffer size, leading to an out-of-bounds write condition when subsequent disk read operations occur.
Critical Impact
This vulnerability enables arbitrary code execution through heap memory corruption, potentially allowing attackers to bypass Secure Boot mechanisms and compromise system integrity at the bootloader level.
Affected Products
- GRUB2 bootloader with UFS module enabled
- Linux distributions using GRUB2 with UFS filesystem support
- Systems with Secure Boot relying on GRUB2 for boot chain integrity
Discovery Timeline
- February 19, 2025 - CVE-2025-0677 published to NVD
- September 18, 2025 - Last updated in NVD database
Technical Details for CVE-2025-0677
Vulnerability Analysis
The vulnerability resides in GRUB2's UFS module, specifically within the grub_ufs_lookup_symlink() function. When processing symbolic links on a UFS filesystem, the module reads the inode's data size field to determine how much memory to allocate for storing the symlink target path. However, the code lacks proper validation to detect integer overflow conditions in the data size value.
An attacker who can craft a malicious UFS filesystem image can set the inode's data size to a value that, when processed, causes an integer overflow. This results in grub_malloc() allocating a buffer that is significantly smaller than the actual data to be read. When the module subsequently reads the symlink content from disk into this undersized buffer, a heap buffer overflow occurs. This heap corruption can be leveraged to achieve arbitrary code execution within the GRUB2 bootloader context.
The exploitation requires local access and the ability to present a malicious filesystem to the bootloader, such as through a removable storage device or a compromised boot partition. Successfully exploiting this vulnerability could allow an attacker to execute arbitrary code before the operating system loads, effectively bypassing Secure Boot protections and establishing persistent compromise.
Root Cause
The root cause is an out-of-bounds write vulnerability (CWE-787) stemming from improper validation of the inode data size field in the UFS module. The code path in grub_ufs_lookup_symlink() does not check whether the symlink data size has overflowed before using it to calculate the allocation size for grub_malloc(). This missing bounds check allows specially crafted filesystem metadata to trigger a heap buffer overflow condition.
Attack Vector
The attack vector requires local access to the system. An attacker must craft a malicious UFS filesystem containing specially constructed inode metadata with an overflowed data size value. This malicious filesystem can be delivered through:
- A crafted bootable USB device or removable media
- A compromised boot partition on the system
- A network boot image served to the target system
When GRUB2 attempts to resolve a symlink on the malicious filesystem during the boot process, the overflow condition triggers, corrupting heap memory and potentially allowing the attacker to redirect execution flow to attacker-controlled code.
Detection Methods for CVE-2025-0677
Indicators of Compromise
- Unusual or unexpected filesystem images present on boot devices
- Unexpected modifications to boot partition contents or GRUB2 configuration
- Boot failures or system instability when processing UFS filesystems
- Evidence of boot chain tampering or Secure Boot violation alerts
Detection Strategies
- Monitor for unauthorized changes to bootloader components and boot partition integrity
- Implement filesystem integrity monitoring for boot-related partitions
- Enable Secure Boot logging and alerting for boot chain verification failures
- Audit boot device access and detect unauthorized removable media connections
Monitoring Recommendations
- Utilize UEFI Secure Boot with properly configured trust chain verification
- Deploy boot integrity measurement solutions to detect bootloader modifications
- Monitor system logs for GRUB2-related errors or crash conditions during boot
- Implement hardware security modules (HSM) or TPM-based measured boot where available
How to Mitigate CVE-2025-0677
Immediate Actions Required
- Apply the latest GRUB2 security updates from your distribution vendor immediately
- Verify Secure Boot is enabled and properly configured on affected systems
- Restrict physical access to systems to prevent malicious boot media attacks
- Audit boot partition integrity and investigate any unauthorized changes
Patch Information
Red Hat has released security advisories addressing this vulnerability. Administrators should apply the following updates:
Additional technical details are available in Red Hat CVE Analysis CVE-2025-0677 and Red Hat Bugzilla Report #2346116.
Workarounds
- Disable UFS filesystem support in GRUB2 if not required for your environment
- Implement strict boot device controls to prevent unauthorized boot media
- Enable UEFI Secure Boot with a revocation list (DBX) update if available from your vendor
- Restrict BIOS/UEFI settings to prevent boot order modifications by unauthorized users
# Verify GRUB2 version and check for updates (Red Hat/CentOS/Fedora)
rpm -q grub2
dnf check-update grub2
# Verify Secure Boot status
mokutil --sb-state
# Check for available GRUB2 updates on Debian/Ubuntu systems
apt list --upgradable | grep grub
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
