CVE-2026-0421 is a BIOS-level vulnerability identified in several Lenovo ThinkPad models including L13 Gen 6, L13 Gen 6 2-in-1, L14 Gen 6, and L16 Gen 2. The root cause is an unchecked return value in the BIOS firmware code that can cause Secure Boot to be disabled despite being set to 'On' in the BIOS setup menu. Secure Boot is a critical security feature designed to ensure that only trusted, signed bootloaders and operating systems are allowed to execute during the system startup process. This vulnerability specifically affects systems configured with Secure Boot in User Mode, a setting that allows user-level control over Secure Boot keys and policies. When Secure Boot is inadvertently disabled, attackers with local access and elevated privileges could install persistent bootkits or rootkits that compromise system integrity at the earliest stage of the boot process. The vulnerability requires local access with high privileges and some user interaction, but does not allow remote exploitation or privilege escalation by itself. The CVSS 4.0 vector indicates low attack vector (local), low attack complexity, no authentication bypass, but high impact on confidentiality, integrity, and availability. No patches or exploits are currently publicly available, but the risk is significant given the critical role of Secure Boot in platform security. Organizations should monitor Lenovo advisories for firmware updates and consider additional endpoint protection measures to detect firmware tampering or unauthorized bootloader modifications.

For European organizations, the disabling of Secure Boot can have severe consequences. Secure Boot is a foundational security control that prevents unauthorized code execution during system startup, protecting against bootkits and rootkits that are notoriously difficult to detect and remove. If Secure Boot is disabled without administrator awareness, attackers could implant persistent malware that survives OS reinstallations and evades traditional antivirus solutions. This undermines the confidentiality, integrity, and availability of critical systems, especially in sectors such as finance, government, healthcare, and critical infrastructure where Lenovo ThinkPads are commonly used. The vulnerability could facilitate advanced persistent threats (APTs) targeting sensitive data or operational technology. Additionally, compliance with European cybersecurity regulations such as NIS2 and GDPR may be impacted if Secure Boot is compromised, leading to potential legal and reputational damage. The requirement for local high-privilege access limits remote exploitation but insider threats or attackers who gain initial footholds could leverage this vulnerability to deepen their control over affected systems.

1. Monitor Lenovo’s official security advisories closely for firmware updates addressing CVE-2026-0421 and apply patches promptly once available. 2. Until patches are released, enforce strict physical and administrative controls to limit local access to affected devices, reducing the risk of exploitation. 3. Regularly verify Secure Boot status through BIOS setup or management tools to detect unexpected changes. 4. Employ endpoint detection and response (EDR) solutions capable of monitoring firmware integrity and boot process anomalies. 5. Use hardware-based security features such as TPM and Intel Boot Guard where available to complement Secure Boot protections. 6. Implement strict user privilege management to minimize the number of users with high-level BIOS access. 7. Conduct regular security audits and firmware integrity checks as part of vulnerability management programs. 8. Educate IT staff and users about the importance of Secure Boot and signs of potential firmware tampering. 9. Consider network segmentation and enhanced monitoring for systems running affected Lenovo ThinkPads to detect lateral movement attempts post-exploitation.