CVE-2026-0421 is a BIOS-level vulnerability affecting Lenovo ThinkPad L13 Gen 6, L13 Gen 6 2-in-1, L14 Gen 6, and L16 Gen 2 models. The root cause is an unchecked return value in the BIOS code that manages Secure Boot state. Secure Boot is a security feature designed to ensure that only trusted firmware and software are loaded during system startup, protecting against boot-level malware and rootkits. This vulnerability can cause Secure Boot to be disabled even when the BIOS setup menu shows it as enabled, but only if Secure Boot is set to User Mode. User Mode Secure Boot allows users to manage keys and settings, which introduces complexity and potential for misconfiguration. The unchecked return value means that an error or unexpected condition in the BIOS code is not properly handled, leading to Secure Boot being silently disabled. Exploitation requires an attacker to have high privileges (administrator or equivalent) and user interaction, such as running a crafted application or script. The CVSS 4.0 score is 7.0 (high), reflecting the significant impact on confidentiality, integrity, and availability if Secure Boot protections are bypassed. No known public exploits or patches are currently available, but the vulnerability is published and reserved since December 2025. This flaw could allow attackers to load unauthorized firmware or bootloaders, undermining system trust and potentially enabling persistent malware that is difficult to detect or remove.

For European organizations, this vulnerability poses a significant risk to endpoint security, especially in environments where Lenovo ThinkPad L13 Gen 6 series devices are widely deployed. Secure Boot is a critical defense against firmware-level attacks, and its silent disablement can allow attackers to install persistent rootkits or bootkits, compromising system integrity and confidentiality. Sectors such as finance, government, healthcare, and critical infrastructure that rely on strong firmware security could be particularly impacted. The requirement for high privileges and user interaction limits remote exploitation but does not eliminate risk from insider threats or malware that gains administrative access. The absence of patches means organizations must rely on compensating controls until updates are available. The vulnerability could also affect compliance with security standards that mandate Secure Boot enforcement. Overall, the impact includes increased risk of persistent compromise, data breaches, and potential disruption of critical services.

Organizations should immediately audit BIOS configurations on affected Lenovo ThinkPad models to verify Secure Boot status and mode. Where possible, switch Secure Boot from User Mode to Standard Mode to reduce risk. Limit administrative privileges strictly and monitor for unauthorized changes to BIOS settings. Employ endpoint detection and response (EDR) tools capable of detecting firmware tampering or unusual boot behavior. Maintain strict control over software installation and user interaction to prevent execution of malicious code requiring high privileges. Engage with Lenovo support channels to track release of BIOS updates or patches addressing this vulnerability. Consider implementing hardware-based attestation or trusted platform modules (TPM) to detect Secure Boot state changes. For critical systems, evaluate temporary isolation or enhanced monitoring until patches are deployed. Document and enforce policies for BIOS security and firmware integrity verification as part of broader endpoint security strategy.