CVE-2026-20861 is a race condition vulnerability categorized under CWE-362, affecting Windows Management Services in Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The vulnerability arises from improper synchronization when multiple threads or processes concurrently access shared resources, leading to inconsistent or unexpected behavior. An authorized local attacker can exploit this flaw to elevate privileges, potentially gaining SYSTEM-level access. The vulnerability impacts confidentiality, integrity, and availability by allowing unauthorized escalation and control over the affected 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), and no user interaction (UI:N). The scope is changed (S:C), meaning the vulnerability affects resources beyond the initially vulnerable component. Although no public exploits are known, the vulnerability poses a significant risk due to the potential for full system compromise. The lack of available patches at the time of publication necessitates immediate attention to mitigate risk through alternative controls. The race condition could be exploited by manipulating timing or resource access sequences to bypass security checks or escalate privileges. This vulnerability is particularly critical in environments where Windows 10 Version 1809 remains in use, especially in enterprise and government sectors where local user accounts exist with limited privileges.

For European organizations, this vulnerability presents a significant risk of local privilege escalation, which can lead to full system compromise. Attackers gaining elevated privileges could access sensitive data, disrupt services, or deploy further malware. Critical infrastructure, government agencies, and enterprises relying on Windows 10 Version 1809 are particularly vulnerable. The impact extends to confidentiality breaches, integrity violations through unauthorized changes, and availability disruptions via potential denial-of-service conditions. Since the attack requires local access, insider threats or compromised endpoints are the primary vectors. The high attack complexity reduces the likelihood of widespread exploitation but does not eliminate risk, especially in environments with many local users or weak endpoint security. European organizations with legacy systems or delayed patch cycles are at increased risk. The vulnerability could also be leveraged as a stepping stone in multi-stage attacks targeting sensitive sectors such as finance, healthcare, and public administration.

1. Prioritize patch deployment as soon as Microsoft releases an official fix for this vulnerability. 2. Restrict local user privileges by enforcing the principle of least privilege and removing unnecessary local accounts. 3. Implement strict access controls and monitor local user activities for anomalous behavior indicative of privilege escalation attempts. 4. Use application whitelisting and endpoint detection and response (EDR) solutions to detect and block suspicious processes exploiting race conditions. 5. Harden Windows Management Services by disabling or limiting its use where possible, especially on systems not requiring this service. 6. Conduct regular security audits and vulnerability assessments focusing on legacy Windows 10 systems to identify and remediate outdated versions. 7. Employ network segmentation to isolate critical systems, reducing the risk of lateral movement post-exploitation. 8. Educate users and administrators about the risks of local privilege escalation and the importance of timely updates. 9. Maintain comprehensive logging and alerting to quickly identify exploitation attempts. 10. Consider upgrading to supported Windows versions with active security updates to reduce exposure to legacy vulnerabilities.