CVE-2025-53500 Overview
CVE-2025-53500 is a stored cross-site scripting (XSS) vulnerability [CWE-79] in the Wikimedia Foundation MediaWiki MassEditRegex extension. The flaw stems from improper neutralization of user-supplied input during web page generation. An attacker can inject persistent JavaScript payloads that execute in the browsers of users who view the affected pages.
The issue affects MassEditRegex versions from 1.39.x before 1.39.12, 1.42.x before 1.42.7, and 1.43.x before 1.43.2. Exploitation requires no authentication and no user interaction, though attack complexity is high.
Critical Impact
Stored XSS enables persistent script execution against MediaWiki users, allowing session theft, credential harvesting, and unauthorized wiki actions performed under the victim's identity.
Affected Products
- MediaWiki MassEditRegex Extension 1.39.x before 1.39.12
- MediaWiki MassEditRegex Extension 1.42.x before 1.42.7
- MediaWiki MassEditRegex Extension 1.43.x before 1.43.2
Discovery Timeline
- 2025-07-03 - CVE-2025-53500 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-53500
Vulnerability Analysis
The MassEditRegex extension for MediaWiki allows privileged users to perform bulk edits across multiple pages using regular expressions. The extension processes user-supplied input and renders portions of that input back into HTML output without sufficient output encoding or context-aware escaping.
Because the tainted content is stored and later rendered when other users load the affected interface, the payload persists across sessions. Any script injected through the vulnerable input path executes in the context of the MediaWiki origin, inheriting the victim's authenticated session cookies and CSRF tokens.
Root Cause
The root cause is a failure to apply HTML entity encoding or safe templating to attacker-controlled strings before insertion into the DOM. The extension trusts input that flows through its regex-driven edit workflow and emits it into page output. Details of the code path and fix are documented in Wikimedia Task T397334 and the corresponding Wikimedia Code Change A117378.
Attack Vector
The vulnerability is remotely exploitable over the network. An attacker submits crafted content containing HTML or JavaScript through the MassEditRegex interface. When another user, typically an administrator reviewing edits, loads the affected page, the injected script runs in their browser and can invoke MediaWiki API endpoints on their behalf.
The vulnerability is described in prose only; no verified proof-of-concept is publicly available at time of writing. Refer to the vendor advisory for technical specifics.
Detection Methods for CVE-2025-53500
Indicators of Compromise
- Unexpected <script> tags, event handlers such as onerror= or onload=, or javascript: URIs stored inside wiki page content or edit summaries produced by MassEditRegex.
- Outbound requests from user browsers to attacker-controlled domains immediately after loading pages edited via MassEditRegex.
- Anomalous MediaWiki API activity, such as bulk edits or permission changes originating from administrator accounts shortly after page views.
Detection Strategies
- Audit MassEditRegex edit history for payloads matching HTML tags, JavaScript event attributes, or encoded script patterns.
- Deploy Content Security Policy (CSP) violation reporting and monitor logs for inline script or unauthorized origin violations on MediaWiki pages.
- Correlate web server logs with authentication events to identify session activity that follows a rendered XSS payload.
Monitoring Recommendations
- Enable MediaWiki AbuseFilter rules that flag edits containing script tags or suspicious HTML in regex replacement fields.
- Forward MediaWiki access logs and CSP reports to a centralized logging platform for retention and hunting.
- Alert on privileged account actions performed from browser user agents shortly after viewing MassEditRegex-authored pages.
How to Mitigate CVE-2025-53500
Immediate Actions Required
- Upgrade the MassEditRegex extension to version 1.39.12, 1.42.7, or 1.43.2, matching the MediaWiki core release in use.
- Restrict masseditregex user rights to a minimal set of trusted administrators until patching is complete.
- Review stored wiki content authored via MassEditRegex for injected scripts and revert or sanitize affected revisions.
Patch Information
Wikimedia Foundation released fixes in MassEditRegex versions 1.39.12, 1.42.7, and 1.43.2. The upstream fix is tracked in Wikimedia Code Change A117378 and Wikimedia Task T397334. Administrators should apply the extension update, clear the MediaWiki cache, and validate that page rendering escapes user-supplied content.
Workarounds
- Disable the MassEditRegex extension in LocalSettings.php until the patched version is deployed.
- Enforce a strict Content Security Policy that blocks inline scripts and untrusted script sources across the MediaWiki origin.
- Limit assignment of the masseditregex permission and require multi-factor authentication for accounts holding it.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
