CVE-2026-0421 Overview
A BIOS vulnerability has been identified in several Lenovo ThinkPad models that could result in Secure Boot being disabled even when explicitly configured as "On" in the BIOS setup menu. This flaw affects the L13 Gen 6, L13 Gen 6 2-in-1, L14 Gen 6, and L16 Gen 2 ThinkPad systems. The vulnerability specifically impacts systems where Secure Boot is configured in User Mode, potentially undermining the security guarantees that Secure Boot is designed to provide.
This vulnerability is classified under CWE-252 (Unchecked Return Value), indicating that the BIOS firmware fails to properly validate return values during the Secure Boot configuration process, allowing the security feature to be silently bypassed.
Critical Impact
Systems configured with Secure Boot enabled may actually boot without Secure Boot protection, potentially allowing unauthorized or malicious code to execute during the boot process.
Affected Products
- Lenovo ThinkPad L13 Gen 6
- Lenovo ThinkPad L13 Gen 6 2-in-1
- Lenovo ThinkPad L14 Gen 6
- Lenovo ThinkPad L16 Gen 2
Discovery Timeline
- 2026-01-14 - CVE-2026-0421 published to NVD
- 2026-01-16 - Last updated in NVD database
Technical Details for CVE-2026-0421
Vulnerability Analysis
This vulnerability represents a Secure Boot Bypass in the BIOS firmware of affected Lenovo ThinkPad devices. The core issue lies in how the BIOS handles Secure Boot configuration when the system is operating in User Mode. Despite the user interface displaying Secure Boot as enabled, the actual boot process may proceed without enforcing Secure Boot validation.
The weakness is categorized as CWE-252 (Unchecked Return Value), suggesting that the firmware code responsible for managing Secure Boot state fails to properly check return values from critical functions, leading to an inconsistent state between the configured setting and actual enforcement.
The local attack vector with high privilege requirements indicates that an attacker would need physical access or administrative privileges on the target system to exploit this vulnerability. However, the impact is significant as Secure Boot is a fundamental security boundary that prevents the execution of unauthorized bootloaders and early-stage malware such as bootkits and rootkits.
Root Cause
The root cause of this vulnerability is an unchecked return value (CWE-252) in the BIOS firmware's Secure Boot configuration handling. When Secure Boot is set to User Mode, the BIOS fails to properly validate critical return values during the boot configuration process, resulting in Secure Boot protection being silently disabled despite appearing enabled in the BIOS setup interface.
Attack Vector
The vulnerability requires local access to the affected system. An attacker with physical access or high-level privileges could exploit this condition to boot untrusted or malicious code that would normally be blocked by Secure Boot. This could enable:
- Installation of persistent bootkits that survive OS reinstallation
- Loading of unsigned or tampered bootloaders
- Bypassing platform integrity verification mechanisms
- Compromising the trust chain from firmware to operating system
The attack is particularly concerning because administrators and users would have no visible indication that their security configuration is not being enforced, as the BIOS interface would still show Secure Boot as enabled.
Detection Methods for CVE-2026-0421
Indicators of Compromise
- Secure Boot status reporting "Off" or "Disabled" at the OS level (e.g., via msinfo32 on Windows or mokutil --sb-state on Linux) while BIOS shows it enabled
- Unexpected boot behavior or the ability to boot unsigned operating systems
- UEFI firmware logs showing Secure Boot validation bypassed during boot sequence
- Presence of unsigned or untrusted boot components executing on systems expected to have Secure Boot protection
Detection Strategies
- Compare BIOS-reported Secure Boot status with operating system-reported status using OS-level tools
- Implement automated compliance checks that verify Secure Boot enforcement state matches configuration
- Monitor for boot anomalies using endpoint detection and response (EDR) solutions that can detect early-stage boot threats
- Audit affected ThinkPad models in your environment against the current BIOS firmware version
Monitoring Recommendations
- Deploy SentinelOne Singularity Platform to detect boot-time threats and firmware anomalies on affected endpoints
- Implement regular BIOS/UEFI firmware version auditing for affected ThinkPad models
- Configure alerts for Secure Boot status changes or discrepancies between configured and enforced states
- Establish baseline firmware configurations and monitor for unauthorized modifications
How to Mitigate CVE-2026-0421
Immediate Actions Required
- Identify all Lenovo ThinkPad L13 Gen 6, L13 Gen 6 2-in-1, L14 Gen 6, and L16 Gen 2 systems in your environment
- Check current BIOS firmware versions and compare against patched versions in the Lenovo security advisory
- Verify Secure Boot status at both the BIOS and operating system levels to detect any discrepancy
- Prioritize BIOS updates for systems handling sensitive data or operating in high-security environments
Patch Information
Lenovo has issued a security advisory addressing this vulnerability. Administrators should consult the Lenovo Security Advisory LEN-210688 for the specific BIOS firmware versions that address CVE-2026-0421 and follow the update procedures for affected ThinkPad models.
BIOS updates should be applied following standard change management procedures, with consideration for the following:
- Schedule updates during maintenance windows to minimize disruption
- Ensure systems are connected to reliable power during firmware updates
- Back up current BIOS settings before applying updates
- Verify successful update completion and re-enable Secure Boot in Standard Mode if supported
Workarounds
- Where possible, configure Secure Boot in Standard Mode rather than User Mode to avoid the vulnerable condition
- Implement additional boot security controls such as BitLocker with TPM to provide defense-in-depth
- Restrict physical access to affected systems until firmware updates can be applied
- Enable chassis intrusion detection where available to alert on physical tampering attempts
# Verify Secure Boot status on Linux systems
mokutil --sb-state
# Check Secure Boot status on Windows (PowerShell)
Confirm-SecureBootUEFI
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
