CVE-2026-20825 is a vulnerability classified under CWE-284 (Improper Access Control) found in Microsoft Windows 10 Version 1809, specifically affecting the Hyper-V virtualization platform. The flaw allows an attacker who already has authorized local access with high privileges (e.g., an administrator) to bypass intended access controls and disclose sensitive information from the system. The vulnerability does not require user interaction and does not impact system integrity or availability, focusing solely on confidentiality. The CVSS 3.1 base score is 4.4, reflecting a medium severity level, with the attack vector being local (AV:L), low attack complexity (AC:L), and requiring privileges (PR:H). The scope remains unchanged (S:U), and the impact is high on confidentiality (C:H) but none on integrity (I:N) or availability (A:N). No known exploits have been reported in the wild, and no patches are currently linked, indicating that remediation may still be pending or in progress. The vulnerability is relevant primarily to systems running the specific Windows 10 build 17763.0, which corresponds to the 1809 release, an older version of Windows 10. Hyper-V is widely used in enterprise environments for virtualization, making this vulnerability particularly relevant for organizations relying on virtual machines for workload isolation and management. The improper access control could allow an attacker with local admin rights to extract sensitive data from the Hyper-V environment, potentially exposing confidential information or system details that could facilitate further attacks. Given the requirement for local high privileges, exploitation is limited to insiders or attackers who have already compromised an account with elevated rights. However, the impact on confidentiality can be significant in sensitive environments. The vulnerability underscores the importance of maintaining up-to-date systems and carefully managing administrative privileges and access to virtualization infrastructure.

For European organizations, the primary impact of CVE-2026-20825 is the potential unauthorized disclosure of sensitive information within virtualized environments running on Windows 10 Version 1809. This could include exposure of confidential business data, intellectual property, or security-related information stored or processed within Hyper-V virtual machines. Organizations in sectors such as finance, healthcare, government, and critical infrastructure that utilize Hyper-V for virtualization may face increased risks of data leakage. Since the vulnerability requires local high privileges, the threat is more pronounced from insider threats or attackers who have already gained elevated access. The lack of impact on integrity and availability limits the risk of system disruption or data manipulation, but confidentiality breaches can still lead to compliance violations under GDPR and damage organizational reputation. The older Windows 10 1809 version is less common in modern deployments but may still be present in legacy systems, increasing risk if these systems are not upgraded or patched. European organizations with legacy IT environments or those slow to adopt newer Windows versions are particularly vulnerable. Additionally, the vulnerability could facilitate lateral movement or further exploitation if attackers leverage disclosed information to escalate privileges or access other systems.

To mitigate CVE-2026-20825, European organizations should prioritize the following actions: 1) Apply security updates and patches from Microsoft as soon as they become available for Windows 10 Version 1809 systems running Hyper-V. 2) Where possible, upgrade affected systems to a supported and more recent Windows 10 or Windows 11 version that does not contain this vulnerability. 3) Restrict local administrative privileges to only trusted personnel and implement strict access controls to limit who can manage Hyper-V environments. 4) Conduct regular audits of Hyper-V configurations and access logs to detect any unauthorized access attempts or suspicious activities. 5) Employ endpoint protection and monitoring solutions capable of detecting privilege escalation or unusual local access patterns. 6) Segment virtualized environments and sensitive workloads to reduce the impact of potential information disclosure. 7) Educate IT staff and administrators about the risks associated with improper access control and the importance of maintaining secure virtualization platforms. 8) Consider implementing additional security layers such as encryption of sensitive data within virtual machines to reduce the impact of potential disclosure. These measures collectively reduce the risk of exploitation and limit the potential damage from this vulnerability.