CVE-2025-21269 is a medium-severity vulnerability affecting Microsoft Windows 10 Version 1809 (build 10.0.17763.0). It is categorized under CWE-41, which relates to improper resolution of path equivalence. This vulnerability specifically impacts the Windows HTML platform, enabling a security feature bypass. The core issue arises from the operating system's failure to correctly resolve and normalize file system paths, allowing an attacker to craft specially designed paths that bypass security checks intended to restrict access or execution. This can lead to unauthorized access to resources or execution of malicious content within the HTML platform context. The vulnerability has a CVSS v3.1 base score of 4.3, indicating a medium severity level. The vector string (AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N) shows that the attack can be performed remotely over the network without privileges but requires user interaction. The impact is limited to confidentiality with no direct effect on integrity or availability. No known exploits are currently in the wild, and no official patches have been linked yet. The vulnerability was reserved in December 2024 and published in January 2025, indicating recent discovery and disclosure. The lack of patches suggests that organizations should be vigilant and consider interim mitigations until updates are available.

For European organizations, this vulnerability poses a moderate risk primarily to confidentiality. Attackers could exploit the improper path resolution to bypass security features in Windows HTML platforms, potentially accessing sensitive information or executing malicious scripts in a user's context. Since the vulnerability requires user interaction, phishing or social engineering campaigns could be used to trigger exploitation. Organizations relying on Windows 10 Version 1809, especially those with legacy systems or delayed patching cycles, are at risk. Confidential data exposure could affect sectors handling sensitive personal data, such as finance, healthcare, and government. Although the vulnerability does not directly impact system integrity or availability, the confidentiality breach could lead to further attacks or data leaks. The absence of known exploits reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits over time. European organizations should prioritize identifying affected systems and preparing for patch deployment once available.

1. Inventory and identify all systems running Windows 10 Version 1809 (build 10.0.17763.0) within the organization. 2. Until an official patch is released, implement strict user awareness training to reduce the risk of social engineering and phishing attacks that could trigger exploitation. 3. Employ application whitelisting and restrict execution of untrusted HTML content or scripts, particularly from external or unverified sources. 4. Use network-level protections such as web filtering and intrusion detection systems to block or alert on suspicious HTML content or unusual path traversal attempts. 5. Monitor logs for unusual file path access patterns or security bypass attempts related to HTML platform components. 6. Plan and test deployment of security updates from Microsoft as soon as they become available, prioritizing critical and sensitive systems. 7. Consider upgrading affected systems to a more recent and supported Windows version where this vulnerability is not present. 8. Implement least privilege principles to limit user permissions, reducing the impact of any successful exploitation.