CVE-2026-24796: CloverBootloader Buffer Overflow Flaw

CVE-2026-24796 Overview

CVE-2026-24796 is an Out-of-bounds Read vulnerability affecting CloverHackyColor CloverBootloader in the MdeModulePkg/Universal/RegularExpressionDxe/Oniguruma modules. The vulnerability is associated with program files regparse.c and allows an attacker with local access to potentially cause a denial-of-service condition by triggering memory access outside the intended buffer boundaries.

Critical Impact

This bootloader vulnerability could enable attackers to crash the boot process or potentially leak sensitive memory contents during the early stages of system initialization, affecting system availability and potentially exposing confidential data stored in adjacent memory regions.

Affected Products

• CloverBootloader versions prior to 5162
• MdeModulePkg/Universal/RegularExpressionDxe/Oniguruma modules within affected CloverBootloader releases

Discovery Timeline

• 2026-01-27 - CVE CVE-2026-24796 published to NVD
• 2026-01-27 - Last updated in NVD database

Technical Details for CVE-2026-24796

Vulnerability Analysis

This vulnerability falls under CWE-125 (Out-of-bounds Read), which occurs when a program reads data from a location outside the intended buffer boundary. In the context of CloverBootloader's Oniguruma regular expression module within regparse.c, improper bounds checking during regex parsing operations can lead to memory access violations.

The vulnerability exists in the regular expression parsing component that CloverBootloader utilizes for pattern matching operations during the boot process. When processing malformed or specially crafted input patterns, the parser may attempt to read memory locations beyond the allocated buffer, resulting in potential information disclosure or application crash.

Given the local attack vector required for exploitation, an attacker would need some form of access to the system to supply malicious input to the vulnerable regex parsing functionality. The primary impact is on system availability, as the vulnerability can cause the bootloader to crash, potentially rendering the system unbootable until the issue is resolved.

Root Cause

The root cause of this vulnerability lies in insufficient boundary validation within the Oniguruma regular expression library's parsing routines in regparse.c. During regex compilation or pattern matching, the code fails to properly verify that memory read operations stay within the bounds of allocated buffers. This can occur when processing complex nested patterns, malformed escape sequences, or edge cases in the regex syntax that cause the parser to miscalculate buffer offsets.

Attack Vector

The attack vector for CVE-2026-24796 requires local access to the system. An attacker would need the ability to influence the input processed by the CloverBootloader's regular expression parser. This could potentially occur through:

• Modifying bootloader configuration files that contain regex patterns
• Exploiting another vulnerability that allows injection of malicious patterns
• Gaining physical access to the system and manipulating boot-time configuration

The attack complexity is relatively low once local access is obtained, as no user interaction or special privileges are required to trigger the vulnerability. The primary impact is a denial-of-service condition affecting system availability, with potential secondary impact on downstream systems that depend on the bootloader.

Detection Methods for CVE-2026-24796

Indicators of Compromise

• Unexpected bootloader crashes or system boot failures without hardware-related causes
• Abnormal memory access patterns or segmentation faults during the boot process
• Modified CloverBootloader configuration files containing unusual or malformed regex patterns
• Boot logs indicating parsing errors or memory access violations in Oniguruma components

Detection Strategies

• Monitor for changes to CloverBootloader configuration files and verify their integrity against known-good baselines
• Implement file integrity monitoring on bootloader components and configuration directories
• Review boot logs for parsing errors, memory violations, or unexpected crashes in regex-related modules
• Deploy endpoint detection solutions capable of monitoring boot-time behavior and detecting anomalies

Monitoring Recommendations

• Enable verbose logging in CloverBootloader where possible to capture detailed error information
• Implement Secure Boot mechanisms to detect unauthorized modifications to bootloader components
• Establish baseline behavior for normal boot sequences to identify deviations
• Configure alerts for repeated boot failures that may indicate exploitation attempts

How to Mitigate CVE-2026-24796

Immediate Actions Required

• Update CloverBootloader to version 5162 or later immediately
• Verify the integrity of existing CloverBootloader configuration files for any signs of tampering
• Restrict physical and administrative access to systems running vulnerable versions
• Review and limit regex patterns used in bootloader configurations to minimize attack surface

Patch Information

The vulnerability has been addressed in CloverBootloader version 5162. Users should update to this version or later to remediate the vulnerability. The fix is available through the GitHub Pull Request #732 which contains the necessary corrections to the Oniguruma regex parsing code.

To update CloverBootloader:

1. Download the latest release (version 5162 or later) from the official CloverHackyColor repository
2. Follow the standard CloverBootloader update procedure for your system
3. Verify the installation completed successfully by checking the bootloader version

Workarounds

• Limit access to systems running vulnerable CloverBootloader versions to trusted administrators only
• Implement Secure Boot to prevent unauthorized bootloader modifications where supported
• Monitor bootloader configuration files for unauthorized changes using file integrity monitoring tools
• Consider using alternative bootloader solutions if immediate patching is not feasible