CVE-2026-20919 is a race condition vulnerability categorized under CWE-362, affecting the Microsoft Windows 10 Version 1809 SMB Server. This vulnerability arises from improper synchronization when multiple concurrent executions access shared resources, leading to a race condition. An attacker with authorized network access and low privileges can exploit this flaw to elevate their privileges, potentially gaining higher system rights. The vulnerability is exploitable remotely over the network (AV:N) but requires high attack complexity (AC:H) and low privileges (PR:L). No user interaction is needed (UI:N), and the scope remains unchanged (S:U). The impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H), meaning an attacker could fully compromise the affected system. Although no public exploits are currently known, the vulnerability is critical due to the potential damage from privilege escalation in networked environments. The affected product is Windows 10 Version 1809 (build 17763.0), which is still present in some enterprise environments. The vulnerability was reserved in December 2025 and published in January 2026. No patches are currently linked, indicating organizations should prioritize updates once available. The flaw specifically targets the SMB Server, a critical service for file sharing and network communication, making it a valuable target for attackers aiming to move laterally or escalate privileges within a network.

For European organizations, the impact of CVE-2026-20919 could be significant, especially for those still running Windows 10 Version 1809 in their IT infrastructure. Successful exploitation allows attackers to elevate privileges remotely, potentially leading to full system compromise, unauthorized data access, and disruption of critical services. This is particularly concerning for sectors such as finance, healthcare, government, and critical infrastructure, where SMB services are commonly used for file sharing and network operations. The high impact on confidentiality, integrity, and availability means sensitive data could be exposed or altered, and systems could be rendered unavailable. Additionally, the network-based attack vector increases the risk of lateral movement within corporate networks, amplifying the threat. The absence of known exploits currently provides a window for proactive mitigation, but the high severity score demands immediate attention to prevent future exploitation. Organizations with legacy systems or delayed patching cycles are at elevated risk.

1. Prioritize patching: Monitor Microsoft security advisories closely and apply patches for Windows 10 Version 1809 SMB Server as soon as they are released. 2. Restrict SMB access: Limit SMB traffic to trusted internal networks only, using network segmentation and firewall rules to block SMB access from untrusted or external sources. 3. Implement network-level authentication and strong access controls to reduce the risk of unauthorized access to SMB services. 4. Employ intrusion detection and prevention systems (IDS/IPS) to monitor for unusual SMB traffic patterns or privilege escalation attempts. 5. Conduct regular audits of systems running Windows 10 Version 1809 to identify and upgrade or isolate legacy systems. 6. Use endpoint protection solutions capable of detecting exploitation attempts targeting race conditions or privilege escalation. 7. Educate IT staff about the risks of race condition vulnerabilities and the importance of timely patch management. 8. Consider disabling SMBv1 and enforcing SMB signing and encryption to enhance SMB security posture.