CVE-2025-6594: MediaWiki XSS Vulnerability

CVE-2025-6594 Overview

CVE-2025-6594 is a Cross-Site Scripting (XSS) vulnerability affecting Wikimedia Foundation's MediaWiki software. The vulnerability exists in the API Sandbox component, specifically within the resources/src/mediawiki.Special.Apisandbox/ApiSandbox.Js file. This improper neutralization of input during web page generation allows attackers to inject malicious scripts that execute in the context of authenticated users' browsers.

Critical Impact

Attackers can execute arbitrary JavaScript code in the browsers of MediaWiki users accessing the API Sandbox, potentially leading to session hijacking, credential theft, or unauthorized actions performed on behalf of victims.

Affected Products

• MediaWiki versions 1.27.0 through 1.39.12 (prior to 1.39.13)
• MediaWiki versions 1.42.x through 1.42.6 (prior to 1.42.7)
• MediaWiki version 1.43.x through 1.43.1 (prior to 1.43.2)
• MediaWiki version 1.44.0

Discovery Timeline

• 2026-02-02 - CVE-2025-6594 published to NVD
• 2026-02-03 - Last updated in NVD database

Technical Details for CVE-2025-6594

Vulnerability Analysis

This Cross-Site Scripting vulnerability stems from insufficient input validation and output encoding in MediaWiki's API Sandbox feature. The API Sandbox is a developer tool that allows users to interactively construct and test API queries against the MediaWiki installation. The vulnerable component, ApiSandbox.Js, fails to properly sanitize user-supplied input before rendering it in the browser context.

The vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation). When user input is reflected or stored without adequate sanitization, it creates an opportunity for attackers to inject malicious JavaScript code that executes when other users interact with the affected page.

Root Cause

The root cause of CVE-2025-6594 lies in improper input handling within the ApiSandbox.Js component. The JavaScript code responsible for rendering API sandbox interactions does not adequately escape or sanitize user-controlled data before inserting it into the DOM. This allows specially crafted input containing JavaScript code to be interpreted and executed by the browser rather than being treated as plain text.

Attack Vector

The attack vector for this vulnerability is network-based, requiring user interaction. An attacker can exploit this vulnerability by crafting a malicious URL or input that, when processed by the API Sandbox feature, injects executable JavaScript into the page. The attack scenario typically involves:

1. The attacker identifies the vulnerable input field or parameter in the API Sandbox interface
2. The attacker crafts a payload containing malicious JavaScript code
3. The attacker delivers the malicious payload to a victim through a phishing link, social engineering, or by embedding it in a shared wiki page
4. When the victim accesses the crafted URL or interacts with the malicious content while authenticated to MediaWiki, the injected script executes in their browser session
5. The malicious script can then steal session cookies, perform actions on behalf of the user, or redirect to credential harvesting pages

For detailed technical information about this vulnerability, refer to the Wikimedia Task T395063.

Detection Methods for CVE-2025-6594

Indicators of Compromise

• Unusual JavaScript execution or DOM manipulation events originating from the API Sandbox pages
• Web application firewall (WAF) logs showing XSS payloads targeting Special:ApiSandbox endpoints
• Browser console errors indicating script injection attempts in MediaWiki installations
• User reports of unexpected behavior or redirects when using the API Sandbox feature

Detection Strategies

• Deploy web application firewall rules to detect common XSS patterns targeting MediaWiki API endpoints
• Implement Content Security Policy (CSP) headers with strict directives to prevent inline script execution
• Monitor server access logs for requests to Special:ApiSandbox containing suspicious encoded characters or script tags
• Enable browser-based XSS auditors and review alerts related to MediaWiki domains

Monitoring Recommendations

• Configure SIEM rules to alert on potential XSS patterns in HTTP request parameters targeting MediaWiki installations
• Implement real-time monitoring of JavaScript errors on MediaWiki pages that may indicate exploitation attempts
• Review authentication logs for session anomalies following user access to API Sandbox functionality
• Deploy endpoint detection solutions to identify malicious script execution in user browsers

How to Mitigate CVE-2025-6594

Immediate Actions Required

• Upgrade MediaWiki installations to patched versions: 1.39.13, 1.42.7, or 1.43.2 depending on your version branch
• Review web server logs for evidence of exploitation attempts targeting the API Sandbox
• Implement Content Security Policy headers to restrict inline script execution as a defense-in-depth measure
• Consider temporarily disabling or restricting access to the API Sandbox feature until patches can be applied

Patch Information

Wikimedia Foundation has released security patches addressing this vulnerability in MediaWiki versions 1.39.13, 1.42.7, and 1.43.2. Organizations running affected versions should prioritize upgrading to the latest patched release within their respective version branch. For detailed patch information and release notes, consult the Wikimedia Task T395063.

Workarounds

• Restrict access to the API Sandbox feature (Special:ApiSandbox) to trusted administrators only using MediaWiki's permission system
• Implement strict Content Security Policy headers that block inline script execution and restrict script sources
• Deploy a web application firewall with XSS protection rules enabled for MediaWiki installations
• Consider disabling the API Sandbox extension entirely if it is not essential to operations until patches can be applied

# Example MediaWiki LocalSettings.php configuration to restrict API Sandbox access
# Add to LocalSettings.php to limit access to trusted groups only
$wgGroupPermissions['*']['apisandbox'] = false;
$wgGroupPermissions['user']['apisandbox'] = false;
$wgGroupPermissions['sysop']['apisandbox'] = true;