CVE-2025-54917 is a security vulnerability identified in Microsoft Windows 10 Version 1809 (build 10.0.17763.0) involving a protection mechanism failure categorized under CWE-693: Protection Mechanism Failure. The vulnerability specifically affects the Windows function MapUrlToZone, which is responsible for mapping URLs to security zones. This mapping is a critical security feature used by Windows to enforce zone-based security policies, such as restricting script execution or downloads from untrusted zones. The flaw allows an unauthorized attacker to bypass these security features remotely over a network without requiring any privileges or authentication, although user interaction is necessary to trigger the exploit. The vulnerability has a CVSS v3.1 base score of 4.3, indicating a medium severity level. The attack vector is network-based (AV:N), with low attack complexity (AC:L), no privileges required (PR:N), but requires user interaction (UI:R). The impact is limited to confidentiality (C:L) with no impact on integrity or availability. There are no known exploits in the wild as of the publication date (September 9, 2025), and no patches have been released yet. The vulnerability's root cause is a failure in the protection mechanism that should enforce security zone policies, potentially allowing attackers to bypass restrictions and gain access to information or perform actions that would otherwise be blocked by zone policies. This could lead to information disclosure or facilitate further attacks by reducing the effectiveness of Windows security zones.

For European organizations, this vulnerability poses a moderate risk primarily due to its ability to bypass security zone protections remotely. Organizations relying on Windows 10 Version 1809 in their infrastructure, especially those with network-facing systems or users who frequently interact with external URLs, could be exposed to targeted attacks that circumvent security controls designed to limit exposure to malicious content. Although the impact on confidentiality is limited and there is no direct integrity or availability compromise, attackers could leverage this bypass to access sensitive information or stage follow-on attacks such as phishing or malware delivery. The requirement for user interaction reduces the risk somewhat but does not eliminate it, especially in environments where social engineering is prevalent. Given that Windows 10 Version 1809 is an older release, some organizations may have already migrated to newer versions, but legacy systems and devices still in use could be vulnerable. The lack of a patch at the time of disclosure means organizations must rely on compensating controls until an official fix is available. The vulnerability could also affect compliance with European data protection regulations if exploited to access personal or sensitive data.

To mitigate this vulnerability, European organizations should first identify and inventory all systems running Windows 10 Version 1809. Until a patch is released, organizations should implement network-level protections such as blocking or filtering suspicious URLs and restricting access to untrusted network zones. Employing endpoint security solutions that monitor and block suspicious URL mappings or unusual network activity can help detect exploitation attempts. User education is critical to reduce the risk of successful user interaction-based exploits; training users to recognize phishing attempts and suspicious links will lower the likelihood of triggering the vulnerability. Additionally, organizations should consider upgrading affected systems to a supported and patched version of Windows 10 or later, as newer versions are less likely to contain this vulnerability. Application whitelisting and strict execution policies can also help limit the impact of any bypass. Monitoring logs for unusual access patterns related to URL zone mappings may provide early detection of exploitation attempts. Finally, organizations should stay alert for official patches or advisories from Microsoft and apply updates promptly once available.