CVE-2026-20865 is a use-after-free vulnerability classified under CWE-416 found in Windows Management Services on Microsoft Windows 10 Version 1809 (build 10.0.17763.0). This vulnerability allows an attacker who already has limited local access (low privileges) to exploit improper memory management in the Windows Management Services component, leading to elevation of privileges. The attacker can leverage this flaw to execute arbitrary code or commands with higher privileges, potentially gaining SYSTEM-level access. The vulnerability does not require user interaction but does require the attacker to have some level of local access, which limits remote exploitation. The CVSS v3.1 score of 7.8 reflects high severity due to its impact on confidentiality, integrity, and availability, combined with the complexity of exploitation (high attack complexity) and the need for low privileges but no user interaction. No known exploits have been reported in the wild, and no official patches have been released at the time of this report. The vulnerability is significant because Windows Management Services is a core component responsible for managing system services, and exploitation could allow attackers to bypass security controls and gain persistent elevated access. The flaw stems from a use-after-free condition, where the system attempts to use memory after it has been freed, leading to undefined behavior exploitable by attackers. Organizations still running Windows 10 Version 1809, which is an older and out-of-mainstream-support version, are particularly vulnerable. This version is often found in legacy systems or environments where upgrading is delayed due to compatibility or operational constraints.

The impact of CVE-2026-20865 on European organizations is significant, especially for those relying on Windows 10 Version 1809 in critical infrastructure, government, finance, healthcare, and industrial sectors. Successful exploitation can lead to full system compromise by elevating privileges from a low-privilege user to SYSTEM level, enabling attackers to install malware, exfiltrate sensitive data, disrupt services, or move laterally within networks. Confidentiality, integrity, and availability of affected systems are all at high risk. Since the vulnerability requires local access, insider threats or attackers who have already gained footholds via other means could leverage this flaw to escalate privileges and deepen their control. The lack of patches increases the window of exposure. European organizations bound by strict data protection regulations (e.g., GDPR) face additional compliance risks if breaches occur. Legacy systems in sectors such as manufacturing or public administration, which may still run Windows 10 1809, are particularly vulnerable. The threat could also impact managed service providers and enterprises with large Windows 10 1809 deployments, potentially causing widespread operational disruption.

1. Upgrade affected systems from Windows 10 Version 1809 to a supported and patched Windows version (e.g., Windows 10 21H2 or later) to eliminate the vulnerability. 2. Until upgrades are feasible, restrict local access to trusted and authorized personnel only, employing strict access controls and monitoring. 3. Implement application whitelisting and endpoint detection and response (EDR) solutions to detect anomalous privilege escalation attempts. 4. Monitor Windows Management Services logs and system event logs for suspicious activity indicative of exploitation attempts. 5. Harden systems by disabling unnecessary services and applying the principle of least privilege to user accounts. 6. Prepare for rapid deployment of official patches once Microsoft releases them by maintaining an up-to-date asset inventory and patch management process. 7. Conduct regular security awareness training to reduce insider threat risks and ensure users understand the importance of reporting unusual system behavior. 8. Employ network segmentation to limit the impact of compromised systems and prevent lateral movement. 9. Use multi-factor authentication and strong credential management to reduce the risk of initial local access by attackers.