CVE-2026-20937 is an information disclosure vulnerability classified under CWE-200 affecting Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The vulnerability resides in Windows File Explorer, where an authorized attacker with local access and low privileges can disclose sensitive information without requiring user interaction. The CVSS v3.1 base score is 5.5, reflecting a medium severity level. The attack vector is local (AV:L), with low attack complexity (AC:L), requiring privileges (PR:L), but no user interaction (UI:N). The scope remains 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 read sensitive data but cannot modify or disrupt system operations. The vulnerability was reserved in December 2025 and published in January 2026, with no known exploits in the wild and no patches currently available. The lack of remote exploitability and the requirement for local privileges limit the attack surface, but the potential for sensitive data exposure remains significant, especially in environments where multiple users share systems or where local access controls are weak. The vulnerability highlights the importance of securing local access and monitoring file system activities within Windows environments.

For European organizations, the primary impact is the unauthorized disclosure of sensitive information, which could include personal data, intellectual property, or confidential business information. This exposure can lead to privacy violations, regulatory non-compliance (e.g., GDPR), and competitive disadvantage. Since the vulnerability requires local access and privileges, insider threats or compromised user accounts pose the greatest risk. Organizations with shared workstations, insufficient endpoint security, or weak access controls are particularly vulnerable. The confidentiality breach could facilitate further attacks, such as social engineering or targeted intrusions. Although integrity and availability are not affected, the loss of confidentiality alone can have severe legal and reputational consequences. Critical sectors such as finance, healthcare, and government agencies in Europe, which handle sensitive data, may face heightened risks. The medium severity rating suggests that while the threat is not immediately critical, timely mitigation is essential to prevent exploitation.

1. Restrict local access to systems running Windows 10 Version 1809 by enforcing strict user account controls and limiting administrative privileges. 2. Implement the principle of least privilege to ensure users have only the necessary permissions to perform their tasks. 3. Monitor and audit local file system access and Windows File Explorer activities to detect unusual or unauthorized data access attempts. 4. Employ endpoint detection and response (EDR) solutions capable of identifying suspicious local behaviors. 5. Isolate sensitive systems and data to minimize exposure in case of compromised local accounts. 6. Prepare for patch deployment by tracking updates from Microsoft and testing them in controlled environments once released. 7. Educate users about the risks of local privilege misuse and enforce strong authentication mechanisms to reduce insider threat risks. 8. Consider upgrading to a supported and patched Windows version if feasible, as Windows 10 Version 1809 is an older release with limited support.