CVE-2026-6862: libefiboot DoS Vulnerability in efivar

CVE-2026-6862 Overview

A flaw was found in libefiboot, a component of efivar. The device path node parser in libefiboot fails to validate that each node's Length field is at least 4 bytes, which is the minimum size for an EFI (Extensible Firmware Interface) device path node header. A local user could exploit this vulnerability by providing a specially crafted device path node. This can lead to infinite recursion, causing stack exhaustion and a process crash, resulting in a denial of service (DoS).

Critical Impact

Local attackers can crash processes that use libefiboot by triggering stack exhaustion through malformed EFI device path nodes, leading to denial of service conditions on affected systems.

Affected Products

• libefiboot (component of efivar)
• efivar package
• Linux distributions using efivar/libefiboot for EFI variable management

Discovery Timeline

• 2026-04-22 - CVE CVE-2026-6862 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-6862

Vulnerability Analysis

This vulnerability stems from improper input validation in the device path node parser within libefiboot. The EFI device path node specification requires that each node header contains at minimum 4 bytes: a 1-byte Type field, a 1-byte SubType field, and a 2-byte Length field. The parser fails to enforce this minimum length requirement before processing node data.

When the parser encounters a malformed device path node with a Length field set to less than 4 bytes (or potentially zero), the parsing logic enters an infinite recursion state. Each recursive call attempts to process the same malformed node or advances improperly through the device path structure, ultimately exhausting the available stack space and causing the process to crash.

The weakness is classified as CWE-674 (Uncontrolled Recursion), indicating that the function does not properly limit recursive calls, making it susceptible to stack exhaustion attacks.

Root Cause

The root cause is missing boundary validation in the device path node parsing routine. The parser does not verify that the Length field of each EFI device path node meets the minimum 4-byte requirement before proceeding with recursive parsing operations. This allows crafted input to create parsing conditions that never terminate, leading to uncontrolled stack growth.

Attack Vector

The attack requires local access and user interaction. An attacker must craft a malicious EFI device path structure with nodes containing invalid Length values (less than 4 bytes) and deliver it to an application using libefiboot for parsing. When the vulnerable parser processes this malformed input, it enters infinite recursion, exhausting the process stack and causing a crash.

This vulnerability is exploited through providing specially crafted device path data to applications that utilize libefiboot's parsing functionality. The malformed input triggers the uncontrolled recursion condition, leading to stack exhaustion and subsequent denial of service.

Detection Methods for CVE-2026-6862

Indicators of Compromise

• Process crashes in applications linked against libefiboot with stack overflow signals
• Unexpected segmentation faults in EFI-related utilities such as efibootmgr or similar tools
• System logs showing repeated crashes of processes that interact with EFI variables

Detection Strategies

• Monitor for abnormal process terminations with stack overflow indicators in applications using libefiboot
• Implement file integrity monitoring on EFI-related configuration files and boot entries
• Deploy endpoint detection rules to identify processes crashing with recursion-related stack exhaustion patterns

Monitoring Recommendations

• Enable crash dump collection for processes using libefiboot to capture forensic evidence of exploitation attempts
• Monitor system stability metrics for unusual patterns of service restarts in EFI-related components
• Review application logs for parsing errors related to malformed device path structures

How to Mitigate CVE-2026-6862

Immediate Actions Required

• Update efivar/libefiboot packages to the latest patched versions when available from your distribution
• Restrict local access to systems where unauthorized users could submit crafted EFI device path data
• Monitor vendor advisories from Red Hat and other distributions for patch availability

Patch Information

Users should check for updates to the efivar package from their Linux distribution. For more information, refer to the Red Hat CVE-2026-6862 Advisory and the Red Hat Bug Report #2459982.

Workarounds

• Limit access to EFI variable manipulation utilities to trusted administrators only
• Implement application sandboxing or resource limits (such as ulimit -s) to contain the impact of stack exhaustion
• Consider temporarily disabling or restricting applications that parse untrusted EFI device path input until patches are applied

# Configuration example: Limit stack size to mitigate impact
# Add to /etc/security/limits.conf or systemd service file
# This limits damage from stack exhaustion but may affect legitimate deep recursion
* hard stack 8192