CVE-2025-61650: Wikimedia CheckUser XSS Vulnerability

CVE-2025-61650 Overview

CVE-2025-61650 is a Cross-Site Scripting (XSS) vulnerability affecting the Wikimedia Foundation CheckUser extension. The vulnerability stems from improper neutralization of input during web page generation within the src/Services/CheckUserUserInfoCardService.php component. This flaw allows attackers to inject malicious scripts that could execute in the context of a privileged user's browser session.

Critical Impact

This XSS vulnerability in the CheckUser extension could allow attackers with high privileges to inject malicious scripts, potentially compromising user sessions or exfiltrating sensitive information displayed in the user info card interface.

Affected Products

• Wikimedia Foundation CheckUser (versions before commit 795bf333272206a0189050d975e94b70eb7dc507)

Discovery Timeline

• 2026-02-03 - CVE-2025-61650 published to NVD
• 2026-02-03 - Last updated in NVD database

Technical Details for CVE-2025-61650

Vulnerability Analysis

This vulnerability exists in the CheckUser extension's user information card service. The affected component, CheckUserUserInfoCardService.php, fails to properly sanitize user-supplied input before rendering it in web page output. This improper neutralization creates an opportunity for Cross-Site Scripting attacks.

The attack requires network access and high privileges to exploit, along with user interaction. While the exploitability is limited due to these constraints, successful exploitation could lead to confidentiality impacts through unauthorized access to sensitive information displayed to privileged CheckUser administrators.

The vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation), which encompasses various forms of XSS attacks where untrusted data is included in web page output without proper validation or escaping.

Root Cause

The root cause of this vulnerability lies in insufficient input validation and output encoding within the CheckUserUserInfoCardService.php file. The service processes user information for display in a card format, but fails to properly escape or sanitize certain input fields before incorporating them into the HTML output. This allows specially crafted input containing JavaScript or HTML to be rendered and executed in the victim's browser.

Attack Vector

The attack vector is network-based, requiring an attacker to have high-level privileges within the system. The exploitation scenario involves:

1. An attacker with elevated privileges crafting malicious input containing XSS payloads
2. The malicious input being processed by the CheckUserUserInfoCardService
3. The unsanitized payload being rendered in the user info card output
4. A victim user viewing the affected page, triggering script execution

Due to the requirement for high privileges and user interaction, the practical exploitability of this vulnerability is limited. The vulnerability mechanism involves unsanitized data being passed through the service layer and rendered directly in the browser. For detailed technical information, refer to the Wikimedia Task T403289 tracking this issue.

Detection Methods for CVE-2025-61650

Indicators of Compromise

• Unusual JavaScript execution patterns originating from CheckUser user info card pages
• Unexpected outbound connections from user browsers when viewing CheckUser interfaces
• Anomalous user input containing script tags or JavaScript event handlers in CheckUser-related data fields

Detection Strategies

• Monitor web application logs for suspicious input patterns containing <script>, javascript:, or event handlers like onerror, onload in CheckUser-related requests
• Implement Content Security Policy (CSP) headers to detect and report inline script execution attempts
• Review audit logs for privileged user actions that involve unusual character sequences in user info card operations

Monitoring Recommendations

• Enable detailed logging for the CheckUser extension to capture all user input processing events
• Configure web application firewall (WAF) rules to alert on XSS payload patterns targeting MediaWiki extensions
• Monitor browser-side security reports if CSP reporting is enabled for your MediaWiki installation

How to Mitigate CVE-2025-61650

Immediate Actions Required

• Update the CheckUser extension to a version containing commit 795bf333272206a0189050d975e94b70eb7dc507 or later
• Review recent CheckUser activity logs for any suspicious input patterns
• Ensure privileged CheckUser accounts are limited to trusted administrators only

Patch Information

Wikimedia Foundation has addressed this vulnerability in commit 795bf333272206a0189050d975e94b70eb7dc507. Administrators should update their CheckUser extension to include this fix. The patch details and tracking information are available in the Wikimedia Task T403289.

Workarounds

• Restrict access to the CheckUser extension to only essential, highly trusted administrators until the patch can be applied
• Implement strict Content Security Policy headers to mitigate the impact of any successful XSS attempts
• Consider temporarily disabling the user info card feature if the extension supports granular feature toggles

# Example: Restrict CheckUser permissions in LocalSettings.php
# Only grant CheckUser rights to highly trusted users until patched
$wgGroupPermissions['checkuser']['checkuser'] = true;
$wgGroupPermissions['checkuser']['checkuser-log'] = true;
# Ensure no additional groups have these permissions