CVE-2026-6862

What it actually does

The flaw is an input-validation error in libefiboot, part of efivar, in the EFI device path node parser. EFI device path nodes have a minimum 4-byte header, but vulnerable parsing logic does not verify that a node's Length field is at least 4 bytes before continuing to parse. A specially crafted device path with an invalid short length can cause the parser to recurse or iterate incorrectly until the process exhausts its stack and crashes. The impact is denial of service against applications or utilities that parse attacker-supplied or otherwise untrusted EFI device path data through libefiboot. There is no indication from the published description that this enables code execution, privilege escalation, or data disclosure.

Why it matters to the business

Systems or workflows that rely on efivar/libefiboot-based tooling may experience local process crashes when malformed EFI device path data is processed. The most likely operational impact is disruption of boot-management, firmware-management, installation, provisioning, or maintenance tasks rather than full system compromise. Because exploitation requires local access or convincing a user/process to parse crafted data, and EPSS is very low with no known exploited status, this should generally be treated as a stability and hardening issue, with higher priority for shared Linux systems, provisioning infrastructure, build images, and endpoints where untrusted local users can run EFI-related tools.

How an attack unfolds

An attacker prepares a malformed EFI device path node where the node Length field is smaller than the required 4-byte EFI device path node header. The attacker then causes a vulnerable program linked against libefiboot to parse that crafted device path. Depending on the exposed workflow, this could involve running a local utility, supplying malformed EFI metadata to a tool, or inducing a user or automated process to process the malformed input. When the vulnerable parser encounters the invalid node length, it fails to reject the structure and enters uncontrolled recursive parsing or equivalent repeated processing. The process stack is exhausted and the affected application crashes, causing a denial of service for that operation. Current public information does not indicate active exploitation, ransomware use, or weaponized exploit maturity.

How to fix it

Update the affected efivar/libefiboot package when a vendor-fixed build becomes available for the relevant Ubuntu release. No fixed version was provided in the input, so use the distribution security advisory and package repository as the source of truth for the corrected package version. Where immediate patching is not possible, reduce exposure by limiting local access to EFI-management utilities, preventing untrusted users from invoking tools that parse EFI device paths, avoiding processing untrusted EFI/device-path data, and applying least-privilege controls around firmware and boot-management workflows. Consider restarting or rerunning any failed maintenance jobs after patching, because the primary impact is process crash rather than persistent compromise.

How to confirm the fix worked

Confirm installed efivar/libefiboot package versions against the Ubuntu security advisory or vendor package changelog for this issue. Verify that applications and utilities linked to libefiboot are using the updated library, especially on long-running systems where processes may need restart to load patched libraries. Where safe and authorized, validate in a non-production test environment by exercising EFI device path parsing with malformed short-length nodes and confirming the patched parser rejects the input without crashing. Review package-manager history to confirm the update was applied successfully, and check system logs for recurring crashes of EFI-related tools after the update.

Typical attack path

1. Obtain local execution capability or access to a workflow that parses EFI device path data using libefiboot.
2. Create a malformed EFI device path node with a Length field smaller than 4 bytes.
3. Provide the crafted device path to a vulnerable utility, script, installer, firmware-management component, or other process linked against libefiboot.
4. Trigger parsing of the malformed device path.
5. Cause infinite recursion or stack exhaustion in the parser.
6. Crash the affected process and disrupt the related boot-management or firmware-management task.

How to detect it

Look for evidence of process crashes rather than network intrusion indicators. Useful sources include systemd journal, kernel logs, apport or crash reporting directories, package-manager logs, endpoint telemetry, and audit logs showing execution of EFI-related tools. Focus on crashes or segmentation faults involving libefiboot, libefivar, efibootmgr, fwupd-related components, bootloader installation tools, installer/provisioning scripts, or administrative maintenance jobs. Correlate crashes with local user activity and recent execution of commands that inspect or modify EFI boot entries or parse device paths. Since the vulnerability causes denial of service and has no known public exploitation maturity in the provided data, absence of unique exploit strings is expected; repeated stack-exhaustion or crash events while parsing EFI data are the strongest available signal.

• libefiboot
• libefivar
• efibootmgr
• fwupd
• fwupdmgr
• grub-install
• segfault.*libefiboot
• segmentation fault.*libefiboot
• stack overflow.*libefiboot
• stack exhaustion
• core dumped.*efibootmgr
• core dumped.*fwupdmgr
• /var/crash/
• /var/lib/systemd/coredump/

What your security team should do

• Track the Ubuntu security advisory for efivar/libefiboot and deploy the first fixed package available for all affected supported releases.
• Prioritize patching on systems with shared local user access, automated provisioning roles, firmware-management workflows, installation media, build pipelines, and administrative workstations that run EFI tooling.
• Restrict execution of EFI and boot-management utilities to trusted administrators until patched.
• Search for recent crashes of processes linked to libefiboot, especially efibootmgr, fwupd-related tooling, bootloader installation utilities, and provisioning scripts.
• Ensure package baselines, golden images, containers, and installation media are rebuilt once fixed packages are available.
• Because this is not currently in the CISA KEV catalog and has very low EPSS, handle as routine-to-moderate priority unless local untrusted users or critical provisioning workflows make denial of service materially disruptive.