CVE-2024-26189 is a high-severity vulnerability affecting Microsoft Windows 10 Version 1809 (build 10.0.17763.0). It stems from improper input validation (CWE-20) within the Secure Boot security feature, which is designed to ensure that only trusted software is loaded during the system startup process. Secure Boot is a critical component of the Windows boot chain that helps prevent unauthorized or malicious code from executing before the operating system loads. The vulnerability allows an attacker to bypass Secure Boot protections, potentially enabling the execution of unsigned or malicious bootloaders or kernel-level code. This bypass can compromise the integrity and trustworthiness of the boot process, leading to full system compromise. The CVSS 3.1 base score is 8.0 (high), with an attack vector of adjacent network (AV:A), low attack complexity (AC:L), no privileges required (PR:N), but requiring user interaction (UI:R). The scope is unchanged (S:U), and the impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H). Although no known exploits are currently in the wild, the vulnerability's nature and impact make it a significant risk, especially for environments where Windows 10 Version 1809 remains in use. The lack of available patches at the time of publication increases exposure. This vulnerability could be exploited by an attacker with network proximity who can trick a user into interacting with a malicious payload, thereby bypassing Secure Boot protections and gaining persistent, low-level control over the system.

For European organizations, the impact of this vulnerability is substantial. Many enterprises and public sector entities still operate legacy Windows 10 Version 1809 systems, especially in critical infrastructure, manufacturing, and government sectors. A successful exploitation could lead to persistent malware infections that survive reboots and evade traditional endpoint security measures, enabling espionage, data theft, ransomware deployment, or sabotage. The high impact on confidentiality, integrity, and availability means sensitive data could be exfiltrated, system integrity undermined, and operational disruptions caused. Given the requirement for user interaction but no privileges, phishing or social engineering campaigns could be effective attack vectors. The vulnerability also poses risks to supply chain security and trusted computing bases, which are vital for compliance with European cybersecurity regulations such as NIS2 and GDPR. Organizations relying on Secure Boot as a foundational security control may find their defenses significantly weakened, increasing the risk of advanced persistent threats (APTs) and targeted attacks.

1. Immediate mitigation should focus on upgrading affected systems to a supported and patched Windows version beyond 1809, as Microsoft typically addresses such vulnerabilities in cumulative updates or newer releases. 2. Where upgrades are not immediately feasible, organizations should enforce strict network segmentation and limit network adjacency to vulnerable systems to reduce exposure. 3. Implement enhanced user awareness training to reduce the risk of successful social engineering or phishing attacks that could trigger exploitation. 4. Employ endpoint detection and response (EDR) solutions capable of detecting anomalous bootloader or kernel-level activity indicative of Secure Boot bypass attempts. 5. Utilize hardware-based security features such as TPM attestation and measured boot to complement Secure Boot and detect unauthorized changes in the boot process. 6. Regularly audit and inventory systems to identify those running Windows 10 Version 1809 and prioritize remediation. 7. Monitor threat intelligence feeds and Microsoft advisories for the release of patches or exploit reports to adapt defenses promptly. 8. Consider implementing application allowlisting and restricting execution of unsigned code where possible to mitigate post-exploitation activities.