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). A use-after-free occurs when a program continues to use a pointer after the memory it points to has been freed, potentially leading to arbitrary code execution or privilege escalation. In this case, an attacker with authorized local access but low privileges can exploit this flaw to elevate their privileges to SYSTEM level, gaining full control over the affected system. The vulnerability does not require user interaction, increasing its risk profile. The CVSS v3.1 base score is 7.8, reflecting high impact on confidentiality, integrity, and availability, but with high attack complexity and requiring local privileges. No public exploit code or active exploitation has been reported yet, but the vulnerability is publicly disclosed and considered critical for legacy Windows 10 installations. The lack of patch links suggests that remediation may require upgrading to a newer Windows version or awaiting a security update from Microsoft. This vulnerability could be leveraged in targeted attacks or lateral movement scenarios within compromised networks.

For European organizations, the impact of CVE-2026-20865 is significant, particularly for those still operating Windows 10 Version 1809 in production environments. Successful exploitation grants attackers SYSTEM-level privileges, enabling them to bypass security controls, access sensitive data, install persistent malware, or disrupt services. This can lead to data breaches, operational downtime, and compliance violations under GDPR and other regulations. Critical sectors such as government, finance, healthcare, and industrial control systems are especially vulnerable due to the potential for high-value targets and sensitive information. The requirement for local access limits remote exploitation but does not eliminate risk, as attackers who gain initial footholds through phishing or insider threats could leverage this vulnerability for privilege escalation. The vulnerability also poses risks in shared or multi-user environments common in enterprise settings.

European organizations should prioritize upgrading systems running Windows 10 Version 1809 to a supported and patched Windows version to eliminate exposure. If immediate upgrade is not feasible, organizations should implement strict access controls to limit local user privileges and restrict access to Windows Management Services. Employ application whitelisting and endpoint detection and response (EDR) solutions to monitor for suspicious privilege escalation attempts. Regularly audit and harden local user accounts, disable unnecessary services, and enforce the principle of least privilege. Network segmentation can reduce the risk of lateral movement if an attacker compromises one system. Stay informed on Microsoft security advisories for any forthcoming patches or mitigations. Additionally, conduct penetration testing and vulnerability assessments focused on privilege escalation vectors to identify and remediate weaknesses proactively.