CVE-2026-20843 is a vulnerability classified under CWE-284 (Improper Access Control) found in the Windows Routing and Remote Access Service (RRAS) component of Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The flaw allows an attacker who already has some level of local privileges to escalate their privileges further, potentially to SYSTEM level, without requiring user interaction. The vulnerability stems from insufficient access control checks within RRAS, which is responsible for routing and remote access capabilities on Windows systems. Exploitation requires local access and some privileges, but no user interaction is needed, making it a potent vector for privilege escalation attacks. The CVSS v3.1 score of 7.8 reflects high impact on confidentiality, integrity, and availability, with low attack complexity and low privileges required. While no public exploits are known yet, the vulnerability's nature suggests it could be leveraged by attackers to gain full control over affected systems, enabling lateral movement, data exfiltration, or disruption of services. The vulnerability was reserved in December 2025 and published in January 2026, but no official patches have been linked at this time.

For European organizations, this vulnerability poses a significant risk, especially to enterprises and critical infrastructure entities that rely on Windows 10 Version 1809 with RRAS enabled. Successful exploitation can lead to full system compromise, allowing attackers to access sensitive data, disrupt services, or move laterally within networks. This is particularly concerning for sectors such as finance, healthcare, government, and telecommunications, where confidentiality and availability are paramount. The requirement for local access limits remote exploitation but insider threats or compromised endpoints could be leveraged to exploit this vulnerability. The lack of known exploits currently provides a window for proactive mitigation, but the high severity score indicates that once exploited, the consequences could be severe, including data breaches and operational disruptions.

1. Restrict local access to systems running Windows 10 Version 1809, especially those with RRAS enabled, to trusted personnel only. 2. Disable the Routing and Remote Access Service on systems where it is not required to reduce the attack surface. 3. Implement strict endpoint security controls and monitoring to detect unusual privilege escalation attempts or suspicious RRAS activity. 4. Apply least privilege principles to user accounts to minimize the privileges available to potential attackers. 5. Prepare to deploy patches promptly once Microsoft releases them for this vulnerability. 6. Conduct regular audits of RRAS configurations and access controls to ensure they adhere to security best practices. 7. Use application whitelisting and behavior-based detection tools to identify exploitation attempts. 8. Educate IT staff about the vulnerability and encourage vigilance for signs of compromise related to privilege escalation.