CVE-2026-20823 is a vulnerability classified under CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor) affecting Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The issue arises from Windows File Explorer improperly exposing sensitive information to an attacker who already has local access and low-level privileges on the system. The vulnerability does not require user interaction and can be exploited with low complexity, but it does not allow modification or disruption of system operations, limiting its impact to confidentiality breaches only. The CVSS v3.1 base score of 5.5 reflects this medium severity, with attack vector local (AV:L), low attack complexity (AC:L), and privileges required (PR:L). The scope remains unchanged (S:U), and the impact is high on confidentiality (C:H), none on integrity (I:N) and availability (A:N). No public exploits or patches are currently known or available, indicating the vulnerability is newly disclosed and not yet weaponized in the wild. The vulnerability likely involves improper access control or information leakage in File Explorer components, potentially exposing file metadata, directory structures, or cached content that should remain protected. Since Windows 10 Version 1809 is an older release, many organizations may have migrated to newer versions, but some legacy systems remain in operation, especially in industrial, governmental, or specialized environments. The vulnerability requires local access, so attackers must have some foothold or physical access to the machine, limiting remote exploitation. However, once exploited, attackers can gather sensitive information that could facilitate further attacks or data exfiltration.

For European organizations, the primary impact of CVE-2026-20823 is the unauthorized disclosure of sensitive information on affected Windows 10 Version 1809 systems. This can lead to breaches of confidentiality, potentially exposing personal data, intellectual property, or internal operational details. Sectors such as finance, healthcare, government, and critical infrastructure, which often retain legacy systems for compatibility reasons, are particularly vulnerable. The vulnerability could aid attackers in reconnaissance or lateral movement within networks if local access is obtained, increasing the risk of subsequent attacks. Although the vulnerability does not affect system integrity or availability, the exposure of sensitive data can have regulatory consequences under GDPR and other privacy laws, leading to fines and reputational damage. The lack of available patches means organizations must rely on compensating controls until updates are provided or systems are upgraded. The medium severity rating indicates a moderate risk that should not be ignored, especially in environments where local access controls are weak or insider threats exist.

To mitigate CVE-2026-20823, European organizations should prioritize upgrading affected Windows 10 Version 1809 systems to supported and patched Windows versions, as this vulnerability is specific to an older release. Until upgrades are feasible, implement strict local access controls, including enforcing strong authentication and limiting user privileges to reduce the risk of unauthorized local access. Employ endpoint detection and response (EDR) solutions to monitor for suspicious activity related to File Explorer or unusual local access patterns. Disable or restrict features in File Explorer that are not essential, potentially reducing the attack surface. Conduct regular audits of systems to identify legacy Windows 10 1809 installations and plan their phased retirement. Educate users about the risks of local access vulnerabilities and enforce policies to prevent unauthorized physical or remote access to endpoints. Additionally, segment networks to limit lateral movement opportunities if local access is compromised. Maintain up-to-date backups and incident response plans to quickly address any data exposure incidents. Finally, monitor Microsoft security advisories for forthcoming patches and apply them promptly once released.