CVE-2026-20821 is a vulnerability classified under CWE-200, indicating an exposure of sensitive information to unauthorized actors. It affects Microsoft Windows 10 Version 1809 (build 10.0.17763.0) specifically within the Windows Remote Procedure Call (RPC) component. The flaw allows an attacker with local access to the system to disclose sensitive information without requiring any privileges or user interaction. The CVSS v3.1 base score is 6.2, reflecting a medium severity level. The attack vector is local (AV:L), with low attack complexity (AC:L), no privileges required (PR:N), and no user interaction (UI:N). The scope is unchanged (S:U), and the impact is high on confidentiality (C:H), with no impact on integrity (I:N) or availability (A:N). This means the attacker can access sensitive data but cannot modify or disrupt system operations. The vulnerability does not currently have any known exploits in the wild, and no patches have been released as of the publication date. The exposure likely stems from improper access controls or information leakage within the RPC mechanism, which is critical for inter-process communication in Windows. Since the vulnerability requires local access, exploitation scenarios include malicious insiders, compromised local accounts, or malware that has already gained foothold on the system. The lack of required privileges or user interaction lowers the barrier for exploitation once local access is achieved. Given the widespread deployment of Windows 10 Version 1809 in enterprise environments, this vulnerability could be leveraged to gather sensitive information that may facilitate further attacks or data breaches.

For European organizations, the primary impact of CVE-2026-20821 is the potential unauthorized disclosure of sensitive information on affected Windows 10 Version 1809 systems. This could include credentials, configuration details, or other confidential data accessible via the RPC mechanism. Such information leaks can aid attackers in lateral movement, privilege escalation, or targeted espionage. Sectors handling sensitive personal data (e.g., finance, healthcare, government) are particularly at risk due to regulatory and reputational consequences. The local access requirement limits remote exploitation but does not eliminate risk from insider threats or malware infections. Since the vulnerability does not affect system integrity or availability, direct disruption is unlikely; however, the confidentiality breach alone can have significant operational and compliance ramifications under GDPR and other European data protection laws. Organizations with legacy systems still running Windows 10 Version 1809 should prioritize assessment and mitigation to prevent data exposure incidents.

1. Restrict local access to Windows 10 Version 1809 systems by enforcing strict access controls, including limiting physical access and using strong authentication mechanisms for local accounts. 2. Employ endpoint detection and response (EDR) solutions to monitor for suspicious local activity, especially unusual RPC calls or attempts to access sensitive information. 3. Harden systems by disabling unnecessary services and RPC endpoints where feasible to reduce the attack surface. 4. Maintain up-to-date antivirus and anti-malware defenses to prevent initial compromise that could lead to local access. 5. Prepare for patch deployment by tracking Microsoft security advisories and testing updates in controlled environments. 6. Conduct regular audits of user privileges and remove or restrict accounts that do not require local system access. 7. Implement network segmentation to isolate critical systems and limit lateral movement opportunities if local compromise occurs. 8. Educate employees about insider threat risks and enforce policies to detect and respond to suspicious behavior. 9. Use application whitelisting to prevent unauthorized software execution that could exploit this vulnerability. 10. Review and enhance logging and alerting mechanisms to detect potential exploitation attempts promptly.