CVE-2024-26240 is a high-severity vulnerability affecting Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The vulnerability is categorized under CWE-20, indicating improper input validation. Specifically, it involves a security feature bypass in the Secure Boot mechanism. Secure Boot is a critical security feature 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 allows an attacker to bypass Secure Boot protections by exploiting improper input validation, potentially enabling the execution of unauthorized code at boot time. The CVSS 3.1 base score is 8.0, reflecting high severity, with the vector indicating that the attack requires adjacent network access (AV:A), low attack complexity (AC:L), no privileges required (PR:N), but does require 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 reported in the wild, the vulnerability poses a significant risk due to its potential to compromise the boot process, which is foundational to system security. The lack of available patches at the time of this report increases the urgency for mitigation and monitoring. Since the vulnerability affects a specific older Windows 10 version (1809), systems running this version remain at risk until remediation is applied.

For European organizations, the impact of this vulnerability is substantial. Many enterprises, government agencies, and critical infrastructure operators still run legacy Windows 10 systems, including version 1809, due to compatibility or operational constraints. A successful exploitation could allow attackers to bypass Secure Boot, leading to persistent malware infections that are difficult to detect and remove, potentially compromising system integrity and confidentiality. This could result in data breaches, espionage, ransomware deployment, or disruption of critical services. The high impact on availability also means that systems could be rendered inoperable, affecting business continuity. Given the requirement for user interaction and adjacent network access, targeted phishing or local network attacks could be vectors for exploitation. The vulnerability is particularly concerning for sectors with high security requirements such as finance, healthcare, energy, and government institutions across Europe. The absence of known exploits currently provides a window for proactive defense, but the potential for rapid weaponization remains.

1. Immediate inventory and identification of all systems running Windows 10 Version 1809 (build 10.0.17763.0) within the organization. 2. Prioritize upgrading or patching affected systems as soon as Microsoft releases an official security update addressing CVE-2024-26240. 3. Until patches are available, consider disabling network access from adjacent networks where possible or segmenting networks to limit exposure. 4. Implement strict user awareness training to reduce the risk of social engineering attacks that could trigger the required user interaction for exploitation. 5. Employ endpoint detection and response (EDR) solutions capable of monitoring boot processes and detecting anomalies indicative of Secure Boot bypass attempts. 6. Enforce multi-factor authentication and least privilege principles to reduce the impact of potential compromise. 7. Regularly audit Secure Boot configurations and verify firmware integrity to detect unauthorized changes. 8. Maintain up-to-date backups and incident response plans tailored to boot-level compromises. These steps go beyond generic advice by focusing on the specific nature of the vulnerability (Secure Boot bypass) and the operational realities of legacy Windows 10 environments.