CVE-2026-20867 is a race condition vulnerability classified under CWE-362 affecting Windows Management Services in 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 inconsistent or unexpected behavior. An authorized local attacker can exploit this race condition to elevate their privileges, potentially gaining SYSTEM-level access. The vulnerability impacts confidentiality, integrity, and availability by allowing unauthorized privilege escalation, which can lead to full system compromise, unauthorized data access, or disruption of services. The CVSS v3.1 score is 7.8 (high), reflecting the need for local access (AV:L), high attack complexity (AC:H), and low privileges required (PR:L), but no user interaction (UI:N). The scope is changed (S:C), indicating that the vulnerability affects resources beyond the initially compromised component. No known exploits are currently in the wild, and no patches have been published yet, increasing the urgency for defensive measures. The vulnerability is particularly critical in environments where Windows 10 1809 remains in use, often due to legacy application dependencies or delayed upgrade cycles. The race condition nature makes exploitation timing-sensitive and complex, but the impact of successful exploitation is severe.

For European organizations, the impact of CVE-2026-20867 can be substantial. Privilege escalation vulnerabilities allow attackers who have gained limited local access—such as through phishing, insider threats, or compromised accounts—to elevate their privileges to SYSTEM level, effectively gaining full control over affected machines. This can lead to unauthorized access to sensitive data, disruption of critical services, and lateral movement within networks. Organizations in sectors such as finance, healthcare, government, and critical infrastructure, which often run legacy Windows 10 versions due to application compatibility, are particularly vulnerable. The vulnerability could facilitate advanced persistent threats (APTs) and insider attacks, undermining data protection and compliance with regulations like GDPR. Additionally, the lack of patches at the time of disclosure increases the risk window. The requirement for local access limits remote exploitation but does not eliminate risk, especially in environments with weak endpoint security or where attackers have already established footholds.

1. Apply official patches from Microsoft immediately once they become available to address this vulnerability. 2. Until patches are released, restrict local access to systems running Windows 10 Version 1809 by enforcing strict access controls and limiting administrative privileges. 3. Implement application whitelisting and endpoint detection and response (EDR) solutions to monitor and block suspicious privilege escalation attempts. 4. Conduct regular audits of user privileges and remove unnecessary local administrator rights. 5. Employ network segmentation to limit lateral movement in case of compromise. 6. Use virtualization-based security features and enable Windows Defender Credential Guard where possible to protect credentials and mitigate privilege escalation. 7. Educate users and administrators about the risks of local privilege escalation and enforce strong authentication mechanisms. 8. Monitor system and security logs for anomalies indicative of race condition exploitation attempts. 9. Plan and execute upgrades to supported Windows versions to reduce exposure to legacy vulnerabilities. 10. Coordinate with incident response teams to prepare for potential exploitation scenarios.