CVE-2026-20923 is a use-after-free vulnerability categorized under CWE-416 affecting Windows Management Services in Microsoft Windows 10 Version 1809 (build 17763.0). This vulnerability arises when the system improperly handles memory, freeing an object while it is still in use, which can lead to arbitrary code execution or privilege escalation. In this case, an attacker with authorized local access but low privileges can exploit the flaw to elevate their privileges to SYSTEM level, gaining full control over the affected machine. The vulnerability does not require user interaction but does require local access and has a high attack complexity, meaning exploitation is non-trivial but feasible. The CVSS 3.1 base score is 7.8, reflecting high impact on confidentiality, integrity, and availability, and the scope is changed, indicating that exploitation affects resources beyond the initially vulnerable component. No public exploits or patches have been released as of the publication date, but the vulnerability is officially published and reserved since December 2025. The lack of patches necessitates immediate attention to mitigate risk. The vulnerability is particularly concerning for environments where Windows 10 Version 1809 remains in use, often in legacy or specialized systems. Attackers exploiting this vulnerability can bypass security controls, install malware, or disrupt operations, posing significant risks to organizational security.

For European organizations, this vulnerability poses a significant risk especially to those still operating Windows 10 Version 1809, which may be prevalent in legacy systems or environments where upgrading is delayed due to compatibility or operational constraints. Successful exploitation can lead to full system compromise, allowing attackers to access sensitive data, disrupt services, or move laterally within networks. Critical infrastructure sectors such as energy, healthcare, finance, and government are particularly vulnerable due to the potential impact on availability and integrity of systems. The local attack vector limits remote exploitation but insider threats or attackers who gain initial local access through other means can leverage this vulnerability to escalate privileges. This elevates the risk profile for organizations with less stringent internal access controls or those lacking robust endpoint monitoring. The absence of known exploits in the wild currently reduces immediate threat but does not eliminate the risk, as weaponization could occur rapidly once details become widely known. The vulnerability's high impact on confidentiality, integrity, and availability underscores the importance of timely mitigation to prevent potential data breaches, operational disruptions, or compliance violations under European data protection regulations.

1. Restrict local access to systems running Windows 10 Version 1809 by enforcing strict access controls and limiting administrative privileges. 2. Monitor systems for unusual privilege escalation attempts or suspicious activity indicative of exploitation attempts. 3. Apply any available security updates or patches from Microsoft immediately upon release; maintain close communication with Microsoft security advisories for updates on this vulnerability. 4. Consider upgrading affected systems to a more recent, supported Windows version where this vulnerability is not present, especially in critical environments. 5. Implement application whitelisting and endpoint detection and response (EDR) solutions to detect and block exploitation attempts. 6. Conduct regular security audits and vulnerability assessments focusing on legacy systems to identify and remediate similar risks. 7. Educate IT staff and users about the risks of local privilege escalation vulnerabilities and the importance of reporting suspicious behavior. 8. Employ network segmentation to limit the impact of compromised systems and prevent lateral movement within the network.