CVE-2025-54917 is a vulnerability classified under CWE-693 (Protection Mechanism Failure) that affects Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The flaw resides in the Windows MapUrlToZone function, which is responsible for determining the security zone of a URL to enforce zone-based security policies. Due to improper handling within this function, an attacker can bypass certain security features remotely over a network. This bypass could allow the attacker to circumvent restrictions typically enforced by zone policies, potentially exposing users to malicious content or actions that would otherwise be blocked. The vulnerability requires no privileges (AV:N), has low attack complexity (AC:L), and does not require authentication (PR:N), but does require user interaction (UI:R), such as clicking a crafted link or opening a malicious file. The scope is unchanged (S:U), and the impact is limited to confidentiality (C:L) with no impact on integrity or availability. The CVSS v3.1 base score is 4.3, indicating a medium severity level. No known exploits have been reported in the wild, and no official patches have been linked at the time of publication. The vulnerability was reserved on July 31, 2025, and published on September 9, 2025. Given the age of Windows 10 Version 1809, which is out of mainstream support, many organizations may not have applied updates or migrated to newer versions, increasing exposure risk. The vulnerability could be leveraged in targeted phishing or network-based attacks to bypass security zones and deliver malicious payloads or steal sensitive information.

For European organizations, the impact of CVE-2025-54917 is primarily a confidentiality risk due to the bypass of security zone protections. This could lead to exposure of sensitive information or enable further exploitation by delivering malicious content that would normally be blocked by zone policies. Organizations still running Windows 10 Version 1809, especially in sectors such as government, healthcare, finance, and critical infrastructure, may face increased risk if attackers exploit this vulnerability to bypass security controls. The requirement for user interaction means social engineering remains a key attack vector. Although the vulnerability does not affect system integrity or availability directly, successful exploitation could be a stepping stone for more severe attacks. The lack of known exploits in the wild currently reduces immediate risk, but the absence of patches and the medium CVSS score indicate that organizations should not ignore this vulnerability. Legacy systems and those with exposed network services are particularly vulnerable. Failure to address this issue could result in data leaks or unauthorized access to sensitive resources.

1. Upgrade affected systems to a supported and fully patched version of Windows 10 or later to eliminate the vulnerability. 2. If upgrading is not immediately possible, restrict network exposure of Windows 10 Version 1809 systems by limiting inbound connections and using network segmentation. 3. Implement strict URL filtering and web content filtering to reduce the risk of users accessing malicious URLs that exploit the MapUrlToZone bypass. 4. Enhance user awareness training focusing on phishing and social engineering tactics to reduce the likelihood of user interaction with malicious content. 5. Employ application whitelisting and endpoint protection solutions capable of detecting suspicious behaviors related to URL zone bypass attempts. 6. Monitor network and endpoint logs for unusual activity indicative of exploitation attempts, such as unexpected URL zone changes or unauthorized access patterns. 7. Regularly review and update security policies related to browser and application zone settings to ensure they are as restrictive as possible without impacting business operations. 8. Coordinate with IT asset management to identify and inventory all systems running Windows 10 Version 1809 to prioritize remediation efforts.