CVE-2025-62699 is a vulnerability in the CheckUser Extension of the Mediawiki platform maintained by the Wikimedia Foundation. The CheckUser Extension is designed to assist administrators in identifying and managing abusive users by providing additional user-related information. The vulnerability allows an unauthorized attacker to gain access to sensitive information without any authentication or user interaction, effectively enabling footprinting of user data or system details that should be protected. The flaw exists in versions prior to 1.39 of the extension, including the master branch before that release. The weakness is categorized as CWE-200, which involves exposure of sensitive information to unauthorized actors, potentially leaking data that could assist in further attacks or reconnaissance. The CVSS 4.0 vector indicates the attack can be performed remotely over the network with low complexity and no privileges required, and the impact affects confidentiality, integrity, and availability to a limited extent. Although no public exploits have been reported, the vulnerability poses a risk to any Mediawiki deployment using the affected extension, especially those hosting sensitive or critical information. The exposure could allow attackers to map user activity or system configurations, aiding in targeted attacks or social engineering campaigns.

For European organizations, this vulnerability could lead to unauthorized disclosure of sensitive user or system information within Mediawiki installations, which are commonly used in government, academic, and public sector environments. Exposure of such data could facilitate targeted attacks, including spear phishing, social engineering, or further exploitation of other vulnerabilities. Confidentiality is primarily impacted, but limited integrity and availability concerns exist due to potential misuse of exposed information. Organizations relying on Mediawiki for collaborative knowledge bases or documentation may face reputational damage and compliance risks, especially under GDPR, if personal data is exposed. The ease of exploitation (no authentication or user interaction required) increases the threat level, making it accessible to a broad range of attackers. Although no known exploits are currently active, the vulnerability's presence in widely used open-source software increases the likelihood of future exploitation attempts. The impact is particularly significant for entities managing sensitive or regulated information through Mediawiki platforms.

To mitigate CVE-2025-62699, European organizations should immediately upgrade the Mediawiki CheckUser Extension to version 1.39 or later, where the vulnerability is resolved. If upgrading is not immediately feasible, restrict access to the CheckUser Extension by implementing strict access controls such as IP whitelisting, VPN-only access, or role-based permissions limiting who can query CheckUser data. Monitor Mediawiki logs for unusual or unauthorized access attempts to the CheckUser functionality. Conduct regular audits of user permissions and ensure that only trusted administrators have CheckUser privileges. Additionally, consider network segmentation to isolate Mediawiki servers from public-facing networks where possible. Organizations should also review their data exposure policies and ensure that sensitive user information is minimized within the platform. Finally, stay informed about any emerging exploits or patches related to this vulnerability by subscribing to Wikimedia Foundation security advisories and relevant threat intelligence feeds.