CVE-2025-21211 is a vulnerability identified in Microsoft Windows 10 Version 1809 (build 10.0.17763.0) that involves a Protection Mechanism Failure, specifically a Secure Boot security feature bypass. Secure Boot is a critical security mechanism designed to ensure that only trusted software is loaded during the system startup process, preventing unauthorized or malicious code from executing before the operating system loads. This vulnerability, classified under CWE-693 (Protection Mechanism Failure), allows an attacker to bypass Secure Boot protections, potentially enabling the execution of malicious bootloaders or kernel-level malware without detection. The CVSS v3.1 base score is 6.8, indicating a medium severity level. The vector details show that the attack requires physical proximity or local access (Attack Vector: Physical), but does not require privileges or user interaction, and it impacts confidentiality, integrity, and availability at a high level. No known exploits are currently reported in the wild, and no patches have been linked yet. The vulnerability could be exploited by an attacker with physical access to the device, for example, by booting from a specially crafted external device or manipulating firmware components to circumvent Secure Boot validation. This undermines the trustworthiness of the boot process, potentially leading to persistent malware infections that are difficult to detect or remove, compromising system integrity and confidentiality.

For European organizations, this vulnerability poses a significant risk especially to sectors relying heavily on Windows 10 Version 1809 systems, such as government agencies, critical infrastructure, financial institutions, and enterprises with legacy systems. The ability to bypass Secure Boot can lead to persistent rootkits or bootkits that evade traditional endpoint security solutions, resulting in potential data breaches, espionage, or sabotage. Given that Secure Boot is a foundational security control for protecting system integrity, its failure could also impact compliance with European data protection regulations like GDPR, especially if the breach leads to unauthorized data access or loss. The requirement for physical access limits remote exploitation but increases the threat in environments where devices are accessible to insiders or during transport and maintenance. The lack of a patch at the time of disclosure means organizations must rely on compensating controls until updates are available, increasing exposure risk.

1. Immediate mitigation should focus on restricting physical access to affected devices to trusted personnel only, including securing laptops and desktops in locked environments. 2. Implement hardware-based security measures such as Trusted Platform Module (TPM) and enable BitLocker drive encryption to protect data even if the boot process is compromised. 3. Monitor and audit boot configurations and firmware integrity regularly using tools like Windows Defender System Guard or third-party firmware integrity checkers. 4. Disable legacy boot options and ensure Secure Boot is enabled and properly configured in UEFI settings to reduce attack surface. 5. Maintain an inventory of devices running Windows 10 Version 1809 and prioritize upgrading to newer, supported Windows versions where this vulnerability is not present or patched. 6. Prepare incident response plans that include detection and remediation of boot-level malware. 7. Stay alert for official patches or updates from Microsoft and apply them promptly once available. 8. Consider implementing endpoint detection and response (EDR) solutions capable of detecting anomalous boot behavior or firmware tampering.