CVE-2024-23176 in MediaWiki
Summary
by MITRE • 09/14/2026
An issue was discovered in the MassMessage extension in MediaWiki before 1.40.2. For a Special:MassMessage?uselang=x-xss URL, the i18n key massmessage-form-page-help allows XSS.
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Analysis
by VulDB Data Team • 09/14/2026
The vulnerability identified in the MassMessage extension for MediaWiki versions prior to 1.40.2 represents a significant security flaw rooted in improper input validation and output encoding mechanisms. This specific issue affects the Special:MassMessage interface, which is designed to allow administrators or authorized users to send messages to multiple recipients simultaneously. The core of the problem lies within the internationalization system, specifically how the application handles language selection parameters passed via URL query strings. When a user constructs a request with a custom locale parameter such as uselang=x-xss, the MediaWiki instance attempts to load corresponding translation files or fallback text for that specific key. In this case, the i18n key massmessage-form-page-help is retrieved and rendered directly into the HTML response without adequate sanitization of the input value itself if it maps to a missing or custom translation entry.
From a technical perspective, this flaw constitutes an instance of Cross-Site Scripting, commonly referred to as XSS. The vulnerability allows an attacker to inject malicious client-side scripts into web pages viewed by other users. In the context of MediaWiki, while many interactions are restricted to authenticated administrators due to the sensitive nature of mass messaging operations, the existence of this vector remains critical because it bypasses standard output encoding practices. When the application processes the uselang parameter, it fails to ensure that any dynamic content derived from user-supplied input is properly escaped before being inserted into the DOM. This oversight enables an attacker to execute arbitrary JavaScript in the context of the victim's browser session, leveraging the trust relationship between the browser and the MediaWiki server.
The operational impact of this vulnerability extends beyond simple script execution. If exploited successfully by a malicious actor with access to create such URLs, it can lead to account hijacking through session cookie theft, allowing the attacker to impersonate legitimate administrators. Furthermore, XSS attacks can be used to perform actions on behalf of the victim without their knowledge, such as modifying site configurations, deleting pages, or spreading malware to other users who view the affected page. In environments where MassMessage is heavily utilized for internal communications or public announcements, this vulnerability could undermine trust in the platform and compromise sensitive information shared through these channels. The ability to execute scripts also facilitates phishing attacks, where attackers can inject fake login forms or deceptive content that mimics legitimate MediaWiki interfaces to steal credentials from unsuspecting users.
This issue is classified under CWE-79, which covers Improper Neutralization of Input During Web Page Generation known as Cross-site Scripting. It aligns with the ATT&CK technique T1059.007, specifically JavaScript execution within a browser environment. The vulnerability highlights a common pitfall in web application development where internationalization features are not rigorously tested for security implications when handling arbitrary string inputs. Developers often assume that language keys are static and safe, but dynamic resolution of these keys based on user input can introduce unexpected injection points if the underlying framework does not enforce strict encoding rules across all output contexts.
To mitigate this vulnerability, organizations running MediaWiki must upgrade to version 1.40.2 or later immediately, as this release includes patches that address the improper handling of the uselang parameter and ensure proper escaping of dynamic content in the MassMessage interface. For environments where upgrading is not immediately feasible, temporary mitigations include restricting access to the Special:MassMessage page through IP whitelisting or authentication controls if such features are available in the current version. Additionally, implementing a Content Security Policy (CSP) can help mitigate the impact of XSS attacks by restricting the sources from which scripts can be loaded and executed. Regular security audits and code reviews focusing on input validation and output encoding practices should also be conducted to prevent similar vulnerabilities in other parts of the application infrastructure.