CVE-2025-59258 is a vulnerability classified under CWE-532, which involves the insertion of sensitive information into log files within Microsoft Windows Server 2019's Active Directory Federation Services (AD FS). Specifically, the vulnerability occurs when AD FS logs contain sensitive data that should not be exposed, such as authentication tokens, credentials, or other confidential information. Because these logs are accessible locally, an unauthorized attacker with local access can read these logs and extract sensitive information, leading to a confidentiality breach. The CVSS 3.1 base score is 6.2 (medium), reflecting that the attack vector is local (AV:L), with low attack complexity (AC:L), no privileges required (PR:N), and no user interaction (UI:N). The scope is unchanged (S:U), and the impact is high on confidentiality (C:H), but no impact on integrity (I:N) or availability (A:N). The exploitability is moderate since local access is required, but no authentication or user interaction is needed. No known exploits have been reported in the wild, and no patches have been linked yet, indicating that mitigation relies on administrative controls and monitoring until an official fix is released. The vulnerability highlights a common security misconfiguration where sensitive data is logged without proper sanitization or protection, increasing the risk of data leakage if log files are accessed by unauthorized users.

For European organizations, this vulnerability poses a significant risk to the confidentiality of sensitive authentication and identity federation data managed by AD FS on Windows Server 2019. Unauthorized local access to sensitive logs could lead to credential theft, unauthorized access to internal systems, or further lateral movement within networks. This is particularly critical for sectors such as finance, government, healthcare, and critical infrastructure, where identity federation services are widely used and sensitive data protection is paramount. The breach of confidentiality could result in regulatory non-compliance under GDPR, leading to legal and financial penalties. Additionally, the exposure of sensitive information could facilitate more sophisticated attacks, including privilege escalation and identity spoofing. Since the vulnerability does not affect integrity or availability, the primary concern remains data leakage and the subsequent risks it entails.

European organizations should implement immediate mitigations including restricting local access to AD FS log files by enforcing strict file system permissions and auditing access to these logs. Administrators should review current logging configurations to identify and minimize logging of sensitive information where possible. Employing log management solutions that support encryption and access controls can reduce the risk of unauthorized log access. Monitoring and alerting on unusual local access patterns to log files can help detect potential exploitation attempts. Until Microsoft releases an official patch, organizations should consider isolating critical AD FS servers and limiting administrative access. Additionally, applying the principle of least privilege for all users and service accounts interacting with AD FS will reduce the attack surface. Regularly reviewing and updating incident response plans to include scenarios involving sensitive data leakage from logs is also recommended.