CVE-2026-20819 is a vulnerability classified under CWE-822 (Untrusted Pointer Dereference) affecting Microsoft Windows 11 Version 25H2 (build 10.0.26200.0). The flaw resides in the Windows Virtualization-Based Security (VBS) Enclave, a security feature designed to isolate sensitive processes and data from the rest of the operating system. The vulnerability occurs when the system improperly dereferences pointers that can be influenced by an authorized local attacker, leading to disclosure of sensitive information stored within the enclave. Since the enclave is intended to protect critical secrets and operations, leaking such information can undermine the security guarantees of VBS. The attack vector requires local access with some level of privileges (PR:L) but does not require user interaction (UI:N). The CVSS v3.1 base score is 5.5, reflecting a medium severity due to the high confidentiality impact (C:H) but no impact on integrity (I:N) or availability (A:N). Exploitation complexity is low (AC:L), and the scope remains unchanged (S:U). No known exploits have been reported in the wild, and no patches have been published at the time of this analysis. The vulnerability was reserved in December 2025 and published in January 2026. The lack of patches means organizations must rely on compensating controls until updates are available.

For European organizations, the primary impact of CVE-2026-20819 is the potential unauthorized disclosure of sensitive information protected by the VBS enclave. This could include cryptographic keys, credentials, or other confidential data used in secure operations. Such leaks can facilitate further attacks, including privilege escalation or lateral movement, especially in environments where VBS is used to harden security. The vulnerability requires local access, so the risk is higher in environments with multiple users or where attackers can gain foothold through other means. Critical sectors such as finance, government, healthcare, and critical infrastructure that rely on Windows 11 with VBS enabled may face increased risk of data breaches. Although integrity and availability are not directly affected, the confidentiality breach can have regulatory and reputational consequences under GDPR and other European data protection laws. The absence of known exploits reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits over time.

1. Limit local access to systems running Windows 11 Version 25H2 with VBS enabled by enforcing strict access controls and user permissions. 2. Monitor and audit local user activities for unusual behavior that could indicate attempts to exploit this vulnerability. 3. Disable or restrict VBS enclave usage on systems where it is not essential, reducing the attack surface. 4. Implement endpoint detection and response (EDR) solutions capable of detecting abnormal pointer dereferencing or enclave-related anomalies. 5. Maintain up-to-date backups and system snapshots to enable recovery if exploitation leads to further compromise. 6. Stay informed about Microsoft security advisories and apply patches promptly once released. 7. Employ application whitelisting and privilege management to minimize the risk of unauthorized code execution that could leverage this vulnerability. 8. Conduct regular security training to raise awareness about local privilege abuse and insider threats. 9. Consider network segmentation to isolate critical systems that utilize VBS from general user environments. 10. Engage in threat hunting focused on enclave-related activities to detect early exploitation attempts.