CVE-2025-26635 is a vulnerability identified in Microsoft Windows 10 Version 1809, specifically affecting the Windows Hello authentication mechanism. The weakness is classified under CWE-1390, which relates to weak authentication implementations. Windows Hello is designed to provide secure biometric or PIN-based authentication to users, enhancing security by replacing traditional passwords. However, this vulnerability allows an authorized attacker—meaning someone with some level of legitimate access—to bypass a security feature remotely over a network. The CVSS 3.1 base score is 6.5, indicating a medium severity level. The vector details show that the attack can be performed remotely (AV:N), requires low attack complexity (AC:L), but the attacker must have high privileges (PR:H) and no user interaction is needed (UI:N). The scope remains unchanged (S:U), and the impact is high on confidentiality and integrity (C:H/I:H), but no impact on availability (A:N). The exploitability is currently theoretical, as no known exploits are reported in the wild. The vulnerability likely allows an attacker with elevated privileges to circumvent Windows Hello protections, potentially gaining unauthorized access to sensitive data or systems without triggering typical authentication controls. Since Windows 10 Version 1809 is an older release, many organizations may have moved to newer versions, but some still operate legacy systems, making this vulnerability relevant for those environments. No patches are currently linked, so mitigation may rely on workarounds or upgrading to a supported version.

For European organizations, the impact of this vulnerability can be significant, especially in sectors where Windows 10 Version 1809 remains in use, such as government agencies, healthcare, manufacturing, and critical infrastructure. The ability for an authorized attacker to bypass Windows Hello could lead to unauthorized access to confidential information, intellectual property theft, or manipulation of data integrity. This could undermine trust in authentication mechanisms and potentially facilitate lateral movement within networks. Given the high confidentiality and integrity impact, sensitive personal data protected under GDPR could be exposed or altered, leading to regulatory penalties and reputational damage. The lack of availability impact means systems remain operational, but the silent bypass of authentication controls increases the risk of stealthy intrusions. Organizations relying on Windows Hello for secure authentication should be particularly cautious, as this vulnerability weakens a core security feature. The absence of known exploits reduces immediate risk but does not eliminate the threat, especially if attackers develop exploits in the future.

1. Upgrade affected systems from Windows 10 Version 1809 to a more recent, supported Windows version where this vulnerability is patched or not present. 2. Until upgrades are possible, restrict network access to systems running the vulnerable version, especially limiting access to users with high privileges. 3. Implement network segmentation and strict access controls to minimize the risk of an attacker with elevated privileges exploiting this vulnerability remotely. 4. Monitor authentication logs and Windows Hello usage patterns for anomalies that could indicate bypass attempts or suspicious activity. 5. Employ multi-factor authentication (MFA) solutions independent of Windows Hello to add an additional layer of security. 6. Stay alert for official patches or security advisories from Microsoft and apply them promptly once available. 7. Conduct regular security assessments and penetration testing focusing on authentication mechanisms to detect potential weaknesses. 8. Educate privileged users about the risks and encourage minimizing the use of high-privilege accounts for routine tasks.