CVE-2025-61650 in CheckUser
Summary
by MITRE • 02/03/2026
Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting') vulnerability in Wikimedia Foundation CheckUser. This vulnerability is associated with program files src/Services/CheckUserUserInfoCardService.Php.
This issue affects CheckUser: from * before 795bf333272206a0189050d975e94b70eb7dc507.
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Analysis
by VulDB Data Team • 02/04/2026
The CVE-2025-61650 vulnerability represents a critical cross-site scripting flaw within the Wikimedia Foundation's CheckUser extension, specifically within the CheckUserUserInfoCardService.Php file. This vulnerability falls under the CWE-79 category of Cross-Site Scripting, where improper input sanitization allows malicious actors to inject malicious scripts into web pages viewed by other users. The affected component is part of Wikimedia's user information tracking system, which is designed to monitor and log user activities across the Wikimedia platforms. The vulnerability exists in versions prior to the commit hash 795bf333272206a0189050d975e94b70eb7dc507, indicating a specific codebase state where input validation mechanisms were insufficient to prevent malicious payload injection.
The technical flaw manifests when the CheckUser extension processes user input during the generation of web page content for user information cards. The service fails to properly sanitize or escape user-provided data before incorporating it into dynamically generated HTML content, creating an avenue for attackers to execute malicious scripts in the context of other users' browsers. This type of vulnerability is particularly dangerous because it can be exploited through various vectors including user comments, usernames, or other input fields that are displayed within the extension's user interface. The flaw operates at the application layer and can be categorized under the ATT&CK technique T1566.001 for initial access through malicious web content, making it a significant threat to the integrity of user sessions and data within the Wikimedia ecosystem.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to hijack user sessions, steal sensitive information, or manipulate user experiences within the Wikimedia platform. The CheckUser extension is designed for administrative monitoring purposes, making this vulnerability particularly concerning as it could allow attackers to gain unauthorized access to user tracking data or potentially escalate privileges within the system. The vulnerability affects not only individual users but also the overall security posture of Wikimedia projects that rely on this extension for user activity monitoring. Given that the extension is used across multiple Wikimedia projects, exploitation could potentially compromise data integrity across numerous platforms, with implications for user privacy and platform security. The vulnerability's impact is amplified by the fact that it affects a core monitoring extension that is likely integrated into the administrative interfaces of various Wikimedia properties.
Mitigation strategies for CVE-2025-61650 should prioritize immediate deployment of the patched version containing the commit 795bf333272206a0189050d975e94b70eb7dc507 or equivalent security fixes. Organizations should implement comprehensive input validation and output encoding mechanisms to prevent malicious script injection, particularly for all user-provided content that is displayed in web interfaces. The fix should include proper HTML escaping of all dynamic content and implementation of Content Security Policy headers to limit script execution capabilities. Security teams should conduct thorough code reviews of similar components within the CheckUser extension and other Wikimedia projects to identify and remediate potential similar vulnerabilities. Additionally, implementing web application firewalls and monitoring for suspicious input patterns can provide additional layers of protection. The vulnerability serves as a reminder of the importance of secure coding practices and input validation in web applications, particularly for extensions that handle sensitive user data and administrative functions, aligning with security best practices outlined in OWASP Top Ten and NIST cybersecurity frameworks.