CVE-2025-61647 identifies a vulnerability in the Wikimedia Foundation's CheckUser extension, specifically within the source file src/Api/Rest/Handler/UserInfoHandler.php. CheckUser is a MediaWiki extension used primarily by Wikimedia projects to allow trusted users to access sensitive information about user accounts, such as IP addresses and usage patterns, to detect abuse and sockpuppet accounts. The vulnerability affects specific versions identified by commit hashes a3dc1bbcc33acbcca6831d6afaccbb1054c93a57 and 0584eb2ad564648aa3ce9c555dd044dda02b55f4. According to the CVSS v4.0 vector, the vulnerability has an attack vector of network (AV:N), low attack complexity (AC:L), requires privileges (PR:L), and user interaction (UI:A). The impact on confidentiality is low (VC:L), with no impact on integrity or availability. The overall CVSS score is 0.3, indicating a low-severity issue. No known exploits are currently in the wild, and no official patches have been linked yet. The vulnerability likely involves a minor information disclosure or improper handling of user information within the REST API handler, which could allow limited unauthorized access or leakage of user data under certain conditions. Given the nature of CheckUser, which is restricted to trusted users, the risk is mitigated by existing access controls. However, the presence of user interaction and required privileges means exploitation is not trivial. The vulnerability is publicly disclosed and assigned a CVE, indicating it should be addressed in future updates.

For European organizations, the impact of CVE-2025-61647 is limited due to the low severity and the nature of the CheckUser extension, which is typically restricted to trusted Wikimedia or MediaWiki administrators. Confidentiality could be marginally affected if an attacker with some privileges and user interaction manages to exploit the vulnerability, potentially gaining access to sensitive user information such as IP addresses or account details. However, there is no impact on data integrity or system availability. Organizations running private MediaWiki instances with CheckUser enabled, especially those involved in Wikimedia projects or similar communities, could face minor risks of information leakage. The lack of known exploits and the requirement for privileges and user interaction further reduce the likelihood of widespread impact. Nevertheless, any unauthorized access to user data could have privacy implications under GDPR and other European data protection regulations, necessitating careful monitoring and timely patching.

1. Restrict access to the CheckUser extension strictly to trusted and authorized administrators to minimize the risk of exploitation. 2. Monitor official Wikimedia Foundation channels and repositories for patches or updates addressing CVE-2025-61647 and apply them promptly once available. 3. Review and audit user permissions regularly to ensure that only necessary personnel have privileges to use CheckUser features. 4. Implement network-level controls such as IP whitelisting or VPN access for administrative interfaces exposing CheckUser functionality. 5. Enable detailed logging and monitoring of CheckUser API usage to detect any anomalous or unauthorized access attempts. 6. Educate administrators about the potential risks and encourage cautious handling of user information accessed via CheckUser. 7. Consider temporarily disabling or limiting CheckUser REST API endpoints if feasible until a patch is applied. 8. Conduct internal security assessments focusing on REST API handlers and privilege escalation vectors within MediaWiki deployments.