CVE-2026-6862: 
Linux Debian vulnerability analysis and mitigation

CVE-2026-6862 is a denial-of-service vulnerability in libefiboot, a component of the efivar library, caused by uncontrolled recursion (CWE-674) in the device path node parser. The parser fails to validate that each node's Length field is at least 4 bytes — the minimum size for an EFI device path node header — allowing a crafted node to trigger infinite recursion, stack exhaustion, and process crash. The vulnerability was published on April 22, 2026, and affects libefiboot as packaged in Ubuntu and Red Hat-based distributions. It carries a CVSS v3.1 base score of 5.5 (Medium) (Github Advisory, Red Hat Bugzilla).

The root cause is classified as CWE-674 (Uncontrolled Recursion). The device path node parser in libefiboot does not enforce a minimum Length field check (≥ 4 bytes) before recursing into child nodes. A crafted device path node with Length < 4 triggers infinite recursion in the call chain efi_loadopt_is_valid() → efi_loadopt_optional_data_size(), ultimately exhausting the process stack. The attack vector is local, requires no privileges, but does require user interaction (e.g., a user or process parsing a malicious device path input). The suggested upstream fix is a simple guard: if (dp->length < 4) return -1; (Red Hat Bugzilla, Github Advisory).

Successful exploitation results in a denial-of-service condition: the affected process crashes due to stack exhaustion caused by infinite recursion. There is no impact on confidentiality or data integrity — only availability is affected. The scope is limited to the crashing process and does not enable lateral movement or privilege escalation (Github Advisory, Red Hat Bugzilla).

There is no known public proof-of-concept exploit and no evidence of in-the-wild exploitation at this time. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. The EPSS score is approximately 0.013% (0.019% per GitHub Advisory), indicating a very low probability of exploitation in the near term (Github Advisory, Feedly).

1. Craft a malicious device path node: Construct an EFI device path node binary blob where the Length field is set to a value less than 4 bytes (e.g., Length = 2 or Length = 0), violating the minimum EFI device path node header size requirement.
2. Deliver the crafted input: As a local user (no privileges required), provide the malicious device path node to a process or utility that uses libefiboot for parsing — for example, a boot manager tool or EFI variable manipulation utility that calls efi_loadopt_is_valid().
3. Trigger infinite recursion: The parser, lacking a minimum-length guard, recurses indefinitely through efi_loadopt_is_valid() → efi_loadopt_optional_data_size() without a base case, consuming stack frames until the stack is exhausted.
4. Achieve denial of service: The target process crashes with a stack overflow, resulting in a denial-of-service condition for any functionality dependent on that process (Red Hat Bugzilla, Github Advisory).

• Logs: Unexpected process crash logs or segmentation fault entries (SIGSEGV) in system logs (/var/log/syslog, journalctl) associated with EFI-related utilities (e.g., efibootmgr, fwupd).
• Process: Abnormal termination of processes that invoke libefiboot parsing functions, particularly those calling efi_loadopt_is_valid() or related EFI variable utilities.
• File System: Presence of unusually crafted EFI device path binary files or EFI variable data with Length fields set to values less than 4 bytes in EFI variable storage or boot configuration files.

Vendors have not yet released a patched version of efivar/libefiboot as of the disclosure date; the GitHub Advisory lists affected and patched versions as "Unknown" (Github Advisory). The upstream suggested fix is to add a minimum-length guard in the parser: if (dp->length < 4) return -1; (Red Hat Bugzilla). As interim mitigations, organizations should restrict local user access to systems running vulnerable versions of libefiboot/efivar, monitor for unexpected process crashes in EFI-related utilities, and limit which users can interact with EFI device path parsing functionality. Monitor Red Hat and Ubuntu security advisories for patch availability.

The vulnerability was reported to Red Hat's Product Security via OSIDB and tracked in Red Hat Bugzilla (Bug 2459982). The GitHub Advisory Database published the advisory on April 22, 2026, with a "Moderate" severity rating. No significant public researcher commentary or media coverage has been identified beyond standard vulnerability database entries.