CVE-2025-0690 Overview
CVE-2025-0690 is an integer overflow vulnerability in GNU GRUB's read command that can lead to an out-of-bounds write in a heap-based buffer. The vulnerability exists in how GRUB handles keyboard input length tracking during the read operation. When processing user input, GRUB maintains the input length in a 32-bit integer value, which is subsequently used to reallocate the line buffer for accepting additional characters. By providing an exceptionally large input, an attacker can cause this integer value to overflow, resulting in a heap-based buffer overflow condition that could corrupt GRUB's internal critical data structures and potentially bypass Secure Boot protections.
Critical Impact
This vulnerability could allow attackers with physical access to corrupt GRUB's internal data structures and potentially bypass Secure Boot, compromising the boot integrity chain on affected systems.
Affected Products
- GNU GRUB (versions prior to patched releases)
- Linux distributions using vulnerable GRUB bootloader versions
- Systems relying on Secure Boot with unpatched GRUB installations
Discovery Timeline
- 2025-02-24 - CVE-2025-0690 published to NVD
- 2025-05-13 - Last updated in NVD database
Technical Details for CVE-2025-0690
Vulnerability Analysis
This vulnerability is classified as CWE-787 (Out-of-bounds Write) and stems from an integer overflow condition in GRUB's input handling mechanism. The read command in GRUB is responsible for capturing keyboard input from users, particularly during interactive boot menu operations or GRUB shell sessions.
The flaw occurs in the input buffer management logic. As the user types characters, GRUB tracks the current input length using a 32-bit signed or unsigned integer. This length value is used to determine when and how to reallocate the line buffer to accommodate additional input. When the input reaches a size large enough to cause the 32-bit integer to wrap around (overflow), the subsequent memory allocation calculations become incorrect.
The integer overflow leads to a smaller-than-expected buffer being allocated while GRUB continues to write input data, resulting in a classic heap-based out-of-bounds write condition. An attacker exploiting this vulnerability could overwrite adjacent heap memory, potentially corrupting critical GRUB data structures used in the boot process.
The attack requires physical access to the machine and elevated privileges (access to GRUB shell or boot menu), along with user interaction to input the malicious data. While these prerequisites limit remote exploitation, the potential to bypass Secure Boot makes this vulnerability significant for organizations relying on firmware-level security controls.
Root Cause
The root cause is improper handling of integer boundaries in GRUB's input length tracking. The 32-bit integer used to store the input length does not have adequate overflow checks before being used in buffer reallocation calculations. When the length counter wraps around due to overflow, subsequent memory operations use an incorrect (much smaller) size value, leading to heap corruption when the actual input data exceeds the allocated buffer size.
Attack Vector
The attack vector requires physical access to the target system. An attacker must be able to interact with the GRUB bootloader interface, either through the GRUB shell or by manipulating the boot menu input. The exploitation process involves:
- Accessing the GRUB command line interface or a context where the read command processes user input
- Providing extremely large input to trigger the integer overflow condition in the length tracking variable
- Continuing to provide input that overwrites heap memory beyond the allocated buffer
- Leveraging the corrupted memory state to manipulate GRUB's behavior, potentially bypassing Secure Boot validation
The physical access requirement and need for high privileges significantly limits exploitation scenarios to situations where an attacker has direct access to the target hardware, such as insider threats, stolen devices, or targeted attacks against specific machines.
Detection Methods for CVE-2025-0690
Indicators of Compromise
- Unexpected GRUB crashes or boot failures following physical access to systems
- Unusual activity or modifications detected in boot-related logs
- Evidence of Secure Boot bypass or unauthorized kernel loading
- Anomalous heap memory corruption patterns in GRUB debug logs if enabled
Detection Strategies
- Monitor for unauthorized physical access to systems, particularly servers and workstations in sensitive environments
- Implement firmware integrity monitoring to detect unauthorized modifications to GRUB components
- Review system logs for boot anomalies or unexpected GRUB behavior following physical access events
- Deploy endpoint detection solutions capable of monitoring pre-boot environment integrity
Monitoring Recommendations
- Enable UEFI Secure Boot logging where available to track boot component validation
- Implement physical security controls and access logging for critical systems
- Configure alerts for unexpected boot failures or GRUB-related errors in system event logs
- Consider deploying measured boot solutions that can detect boot chain modifications
How to Mitigate CVE-2025-0690
Immediate Actions Required
- Apply the latest GRUB security patches from your Linux distribution vendor immediately
- Review and restrict physical access to critical systems until patches are applied
- Ensure Secure Boot is properly configured with updated revocation lists (DBX)
- Consider implementing additional boot integrity verification mechanisms
Patch Information
Security patches addressing CVE-2025-0690 are available from major Linux distribution vendors. Red Hat has released RHSA-2025:6990 addressing this vulnerability. Organizations should consult their respective Linux distribution security advisories for specific patch versions and installation instructions. The GNU GRUB development mailing list contains additional technical details about the fix.
Additional resources:
Workarounds
- Restrict physical access to systems until patches can be applied
- Implement strong BIOS/UEFI passwords to prevent unauthorized boot menu access
- Disable GRUB command line access where operationally feasible by setting a GRUB password
- Consider enabling UEFI Secure Boot with properly configured trust anchors to limit bootloader modifications
# Set GRUB password to restrict command line access (example)
grub2-setpassword
# Update GRUB configuration after security changes
grub2-mkconfig -o /boot/grub2/grub.cfg
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
