CVE-2024-21371 is a high-severity elevation of privilege vulnerability affecting Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The underlying issue is a Time-of-check Time-of-use (TOCTOU) race condition, classified under CWE-367. This type of vulnerability arises when a system checks a condition (such as permissions or resource state) and then uses the resource based on that check, but the state changes between the check and the use, allowing an attacker to exploit the timing window. In this case, the flaw resides in the Windows kernel, which is a critical component responsible for managing system resources and enforcing security boundaries. An attacker with low privileges (PR:L) but local access (AV:L) can exploit this race condition to elevate their privileges to a higher level, potentially SYSTEM or kernel-level privileges, without requiring user interaction (UI:N). The vulnerability impacts confidentiality, integrity, and availability (all rated high), meaning that successful exploitation could allow an attacker to gain unauthorized access to sensitive data, modify system files or configurations, and disrupt system operations. The attack complexity is high (AC:H), indicating that exploitation requires precise timing and conditions, reducing the likelihood of widespread automated exploitation. There are no known exploits in the wild at the time of publication, and no patches have been linked yet, which means organizations should be vigilant and prepare for remediation once available. The vulnerability is scoped to Windows 10 Version 1809, a legacy version of Windows 10, which may still be in use in some enterprise environments. The CVSS vector reflects that the attack requires local access and low privileges but no user interaction, emphasizing the need for strict local access controls and monitoring. Overall, this vulnerability represents a significant risk for environments running this specific Windows version, especially where local user accounts have limited privileges but could leverage this flaw to gain full control over the system.

For European organizations, the impact of CVE-2024-21371 could be substantial, particularly in sectors where legacy Windows 10 Version 1809 systems remain operational, such as manufacturing, healthcare, and government institutions with slower upgrade cycles. Successful exploitation could allow attackers to bypass security controls, access sensitive personal data protected under GDPR, and disrupt critical business processes. The elevation of privilege could facilitate deployment of ransomware, data exfiltration, or persistent backdoors, undermining confidentiality, integrity, and availability of IT systems. Given the high integrity and availability impact, critical infrastructure and industrial control systems running this Windows version could face operational disruptions. The lack of known exploits currently reduces immediate risk, but the high severity and kernel-level nature of the vulnerability mean that once exploit code becomes available, rapid exploitation attempts are likely. European organizations must consider the regulatory implications of a breach involving personal or sensitive data and the potential reputational damage from successful attacks leveraging this vulnerability.

1. Immediate mitigation should focus on identifying and inventorying all systems running Windows 10 Version 1809 within the organization. 2. Restrict local access to these systems to only trusted personnel and enforce strict access controls and monitoring to detect suspicious activities indicative of exploitation attempts. 3. Implement application whitelisting and endpoint detection and response (EDR) solutions capable of detecting unusual privilege escalation behaviors. 4. Prepare for patch deployment by monitoring Microsoft security advisories for the release of a fix and testing patches in controlled environments before widespread rollout. 5. Where possible, accelerate migration from Windows 10 Version 1809 to supported, up-to-date Windows versions that receive regular security updates. 6. Employ network segmentation to isolate legacy systems and limit lateral movement opportunities for attackers who might exploit this vulnerability. 7. Conduct user training to reinforce the importance of local system security and reporting of anomalies, even though user interaction is not required for exploitation. 8. Review and harden local privilege assignments and group policies to minimize the number of users with local privileges that could be leveraged in an attack.