CVE-2026-20923 is a use-after-free vulnerability classified under CWE-416, affecting Windows Management Services in Microsoft Windows 10 Version 1809 (build 17763.0). Use-after-free vulnerabilities occur when a program continues to use memory after it has been freed, potentially leading to arbitrary code execution or privilege escalation. In this case, an authorized attacker with local access and low privileges can exploit the flaw to elevate their privileges to SYSTEM level, gaining full control over the affected system. The vulnerability does not require user interaction but has a high attack complexity, meaning exploitation demands specific conditions or expertise. The CVSS v3.1 score of 7.8 reflects high impact on confidentiality, integrity, and availability, with the scope being changed due to privilege escalation. Although no known exploits are currently in the wild and no patches have been linked, the vulnerability poses a significant risk to systems still running this older Windows 10 version. Windows Management Services is a core component responsible for managing various system services, so compromise here can lead to full system takeover. The vulnerability was reserved in December 2025 and published in January 2026, indicating recent discovery. Organizations using Windows 10 Version 1809 should prioritize mitigation and patching once available to prevent potential exploitation.

For European organizations, this vulnerability poses a serious risk especially in environments where Windows 10 Version 1809 is still in use, such as legacy systems or specialized industrial control systems. Successful exploitation allows attackers to escalate privileges locally, potentially leading to full system compromise, data theft, disruption of services, or deployment of ransomware and other malware. Confidentiality is at risk as attackers can access sensitive data; integrity is compromised as attackers can alter system configurations or software; availability may be affected if attackers disrupt critical services. The threat is particularly concerning for sectors with stringent data protection requirements like finance, healthcare, and government. Additionally, organizations with large numbers of local users or contractors with limited privileges may face increased risk of insider threats or lateral movement. The absence of known exploits in the wild provides a window for proactive defense, but the lack of patches means organizations must rely on interim mitigations.

1. Restrict local access to systems running Windows 10 Version 1809 by enforcing strict access controls and limiting administrative privileges. 2. Apply the principle of least privilege to all user accounts and services to minimize the impact of potential exploitation. 3. Monitor local system activity for unusual privilege escalation attempts or suspicious behavior using endpoint detection and response (EDR) tools. 4. Disable or restrict Windows Management Services if not required for business operations to reduce the attack surface. 5. Prepare for rapid deployment of official patches or updates from Microsoft once they become available. 6. Conduct regular audits of systems to identify and upgrade any remaining Windows 10 Version 1809 installations to supported versions. 7. Implement network segmentation to isolate legacy systems and limit lateral movement opportunities. 8. Educate IT staff and users about the risks associated with local privilege escalation vulnerabilities and the importance of reporting anomalies promptly.