CVE-2026-20867 is a race condition vulnerability classified under CWE-362 that exists in Windows Management Services on Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The flaw arises from improper synchronization when multiple threads or processes concurrently access shared resources, leading to a state where an attacker with authorized local access can manipulate the timing of operations to escalate privileges. This vulnerability allows an attacker with low-level privileges to gain higher privileges, potentially SYSTEM level, thereby compromising the confidentiality, integrity, and availability of the system. The CVSS v3.1 base score is 7.8, indicating high severity, with attack vector local (AV:L), attack complexity high (AC:H), privileges required low (PR:L), no user interaction (UI:N), and scope changed (S:C). The impact metrics are high for confidentiality, integrity, and availability. No public exploits or patches are currently available, increasing the risk window. The vulnerability is particularly dangerous because it can be exploited without user interaction but requires precise timing and local access. This flaw affects legacy Windows 10 systems that are still in use in many enterprise environments, especially those that have not been upgraded or patched. The race condition could be leveraged by malicious insiders or malware that has gained initial foothold to escalate privileges and move laterally or persist within networks.

For European organizations, the impact of CVE-2026-20867 is significant, especially for those still operating Windows 10 Version 1809 in critical sectors such as government, finance, healthcare, and industrial control systems. Successful exploitation can lead to full system compromise, data breaches, disruption of services, and potential lateral movement within networks. This could result in loss of sensitive data, operational downtime, and damage to reputation. Given the high privileges gained, attackers could disable security controls, install persistent malware, or exfiltrate data. The lack of available patches means organizations must rely on compensating controls, increasing operational complexity and risk. The threat is amplified in environments where local user access is less restricted or where insider threats exist. Additionally, compliance with European data protection regulations (e.g., GDPR) could be jeopardized if breaches occur due to this vulnerability.

1. Immediately audit and restrict local user access to systems running Windows 10 Version 1809, ensuring only trusted personnel have local login rights. 2. Apply the principle of least privilege rigorously, removing unnecessary administrative rights from users and service accounts. 3. Implement strict endpoint detection and response (EDR) solutions to monitor for unusual local privilege escalation attempts or suspicious process behavior. 4. Use application whitelisting to prevent unauthorized code execution that could exploit the race condition. 5. Segment networks to limit lateral movement opportunities if an attacker gains local access. 6. Maintain up-to-date backups and incident response plans tailored to privilege escalation scenarios. 7. Monitor official Microsoft channels closely for patches or security advisories and plan immediate deployment once available. 8. Consider upgrading affected systems to supported Windows versions that do not have this vulnerability. 9. Employ system hardening techniques such as disabling unnecessary services and enforcing strong authentication mechanisms for local access. 10. Conduct regular security awareness training to reduce insider threat risks and encourage reporting of suspicious activities.