CVE-2025-11261 Overview
CVE-2025-11261 is a Cross-Site Scripting (XSS) vulnerability affecting Wikimedia Foundation MediaWiki. The vulnerability stems from improper neutralization of input during web page generation in the mediawiki.Language.js file located in resources/src/mediawiki.Language/. This flaw could allow an attacker to inject malicious scripts into web pages served by affected MediaWiki installations.
Critical Impact
Successful exploitation of this XSS vulnerability could enable attackers to execute arbitrary JavaScript in the context of authenticated users' browsers, potentially leading to session hijacking, credential theft, or unauthorized actions on behalf of victims.
Affected Products
- MediaWiki versions prior to 1.39.15
- MediaWiki versions prior to 1.43.5
- MediaWiki versions prior to 1.44.2
Discovery Timeline
- 2026-02-03 - CVE CVE-2025-11261 published to NVD
- 2026-02-03 - Last updated in NVD database
Technical Details for CVE-2025-11261
Vulnerability Analysis
This vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting (XSS). The flaw exists within the MediaWiki Language handling JavaScript module, specifically in the mediawiki.Language.js file. When user-controlled input is processed by this component, insufficient sanitization allows for the injection of malicious script content that gets rendered in the victim's browser.
The vulnerability requires network access for exploitation, meaning an attacker must be able to reach the affected MediaWiki instance. The attack does not require user interaction but does require high-level privileges to execute, which limits the exploitability in most deployment scenarios.
Root Cause
The root cause of CVE-2025-11261 lies in the mediawiki.Language.js resource file's failure to properly sanitize or encode user-supplied input before incorporating it into dynamically generated web page content. This oversight in the MediaWiki Language JavaScript module allows specially crafted input to break out of the expected data context and be interpreted as executable code by the browser.
Attack Vector
The attack vector for this vulnerability is network-based. An attacker with elevated privileges on the MediaWiki platform could craft malicious input that exploits the improper input neutralization in the Language module. When this content is rendered in another user's browser, the injected script executes within the context of the MediaWiki application, inheriting the victim's session privileges.
The vulnerability is documented in Wikimedia's issue tracking system under Task T402077 and Task T406322, which provide additional technical context about the flaw and its remediation.
Detection Methods for CVE-2025-11261
Indicators of Compromise
- Unusual JavaScript execution patterns in browser console logs originating from MediaWiki Language module resources
- Unexpected outbound connections from client browsers while viewing MediaWiki pages
- Modified or suspicious content within Language-related MediaWiki resource files
Detection Strategies
- Implement Content Security Policy (CSP) headers to detect and block unauthorized inline script execution
- Monitor web application logs for suspicious input patterns targeting the mediawiki.Language.js module
- Deploy web application firewall (WAF) rules to detect common XSS payload signatures in requests to MediaWiki instances
Monitoring Recommendations
- Enable detailed logging for MediaWiki resource loading and JavaScript execution
- Configure browser-based XSS auditing tools and monitor CSP violation reports
- Implement real-time alerting for anomalous behavior in MediaWiki Language module requests
How to Mitigate CVE-2025-11261
Immediate Actions Required
- Upgrade MediaWiki installations to patched versions: 1.39.15, 1.43.5, or 1.44.2 or later
- Implement strict Content Security Policy headers to mitigate XSS exploitation risk
- Conduct a security audit of MediaWiki configurations and review any custom Language module modifications
- Review access controls and ensure principle of least privilege for MediaWiki user accounts
Patch Information
Wikimedia Foundation has addressed this vulnerability in MediaWiki versions 1.39.15, 1.43.5, and 1.44.2. Administrators should upgrade to these patched versions immediately. Additional details about the security fixes can be found in the Wikimedia Phabricator tickets T402077 and T406322.
Workarounds
- Deploy a web application firewall (WAF) with XSS detection rules as a temporary protective measure
- Implement strict Content Security Policy headers to prevent execution of injected scripts
- Restrict access to MediaWiki administrative functions and limit users with elevated privileges
- Consider temporarily disabling or restricting access to Language module functionality if feasible in your environment
# Example: Add Content Security Policy header in Apache configuration
# Add to your MediaWiki virtual host or .htaccess file
Header set Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline';"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
