CVE-2026-20843 is a vulnerability classified under CWE-284 (Improper Access Control) found in the Routing and Remote Access Service (RRAS) component of Microsoft Windows 10 Version 1809 (build 10.0.17763.0). RRAS is a networking service that provides routing and remote access capabilities, often used in enterprise environments for VPN and network routing. The vulnerability allows an attacker who already has some level of local access (authorized user with limited privileges) to escalate their privileges to a higher level, potentially SYSTEM or administrator level, without requiring user interaction. This escalation occurs due to insufficient access control checks within RRAS, enabling unauthorized operations that should be restricted. The CVSS v3.1 score of 7.8 indicates a high severity, with attack vector being local (AV:L), low attack complexity (AC:L), requiring privileges (PR:L), no user interaction (UI:N), unchanged scope (S:U), and high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). No known exploits are currently reported in the wild, but the vulnerability is publicly disclosed and can be targeted by attackers with local access. The vulnerability was reserved in December 2025 and published in January 2026, indicating recent discovery. The lack of available patches at the time of reporting means organizations must rely on interim mitigations. Given that Windows 10 Version 1809 is an older but still supported version in some environments, especially in enterprise and industrial contexts, the vulnerability poses a significant risk to systems relying on RRAS for network connectivity and remote access.

For European organizations, this vulnerability can have severe consequences. An attacker with local access, such as a compromised user account or insider threat, could escalate privileges to gain full control over affected systems. This can lead to unauthorized access to sensitive data, disruption of network services, and potential lateral movement within corporate networks. Critical infrastructure sectors relying on RRAS for remote connectivity, including energy, finance, healthcare, and government, could face operational disruptions and data breaches. The high impact on confidentiality, integrity, and availability means that exploitation could result in data theft, system manipulation, or denial of service. The vulnerability's local attack vector limits remote exploitation but does not eliminate risk from phishing, malware, or insider threats that achieve initial local access. European organizations with legacy Windows 10 Version 1809 deployments, especially in regulated industries with strict compliance requirements, may face increased exposure and regulatory consequences if exploited.

1. Apply official security patches from Microsoft as soon as they become available for Windows 10 Version 1809 to address the RRAS access control flaw. 2. Until patches are released, restrict access to RRAS services by limiting membership in local groups that can manage or interact with RRAS. 3. Implement strict local user privilege management, ensuring users have only the minimum necessary rights to reduce the chance of privilege escalation. 4. Monitor event logs and system behavior for signs of local privilege escalation attempts, focusing on RRAS-related activities. 5. Employ endpoint detection and response (EDR) tools capable of detecting anomalous privilege escalation patterns. 6. Consider upgrading affected systems to newer, fully supported Windows versions where this vulnerability is not present. 7. Harden network segmentation to limit lateral movement opportunities if an attacker gains elevated privileges. 8. Conduct user awareness training to reduce risks of initial local access via phishing or social engineering. 9. Review and audit RRAS configurations to ensure no unnecessary services or features are enabled that could increase attack surface.