CVE-2026-103051 in MediaWiki
Summary
by MITRE • 09/30/2026
Improper neutralization of input during web page generation ('cross-site scripting') vulnerability in The Wikimedia Foundation Mediawiki - CentralNotice extension allows Stored XSS.
This issue affects Mediawiki - CentralNotice extension: before 1.46.1, 1.45.5, 1.43.10.
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Analysis
by VulDB Data Team • 09/30/2026
The identified vulnerability represents a critical security flaw within the Wikimedia Foundation's MediaWiki platform, specifically targeting the CentralNotice extension prior to versions 1.46.1, 1.45.5, and 1.43.10. This issue is classified as an improper neutralization of input during web page generation, commonly known as Cross-Site Scripting or XSS. Unlike reflected XSS attacks where malicious scripts are executed via a user's browser through manipulated URLs, this vulnerability allows for Stored XSS. In a stored cross-site scripting attack, the malicious script is permanently stored on the target server, typically within a database, comment field, or other data input mechanisms. When users subsequently request access to the affected page containing the injected payload, the web application retrieves and executes the harmful code in their browsers without any additional manipulation required by the attacker beyond the initial injection phase.
The technical root cause lies in insufficient validation and sanitization of user-supplied input within the CentralNotice extension's handling mechanisms. The extension is responsible for managing banner advertisements and notices displayed across Wikimedia projects, often allowing administrators or specific users to configure content that appears on various pages. If the application fails to properly encode special characters such as angle brackets, quotes, and ampersands before rendering them in HTML context, an attacker can inject executable JavaScript code into these notice configurations. Because CentralNotice is a high-visibility component integrated deeply into the site's frontend infrastructure, any script executed through this vector will run with significant privileges relative to other parts of the application, potentially gaining access to sensitive user sessions or administrative functions depending on the victim's role and permissions.
The operational impact of this vulnerability is severe due to its persistent nature and broad reach. An attacker who successfully exploits this flaw can execute arbitrary JavaScript in the context of any visitor viewing a page where the malicious notice has been stored. This enables a range of malicious activities including session hijacking, where the attacker steals authentication cookies to impersonate legitimate users; keylogging to capture sensitive information such as passwords or personal data entered by victims; and defacement of the website content. Furthermore, because CentralNotice is often used for important announcements across multiple Wikimedia projects, an exploit could be leveraged in a widespread phishing campaign, tricking thousands of users into revealing credentials on a malicious site controlled by the attacker. The trust associated with official Wikimedia domains significantly increases the success rate of such social engineering attacks compared to unknown sources.
From a classification perspective, this vulnerability aligns with CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'). Specifically, it falls under the sub-category of Stored XSS where input is not validated before storage in a database or persistent store. In terms of offensive security frameworks like MITRE ATT&CK, this exploit maps to techniques involving Client-side Injection and potentially Account Manipulation if used for persistence or privilege escalation. The attack vector typically involves Initial Access through social engineering or direct injection by an authenticated user with write permissions on the notice configuration interface, followed by Execution via browser-based script interpretation.
Mitigation strategies must focus primarily on immediate patching of the affected MediaWiki installations to versions 1.46.1, 1.45.5, or 1.43.10 and later, as these releases contain fixes for the input validation logic within the CentralNotice extension. For organizations unable to upgrade immediately due to compatibility constraints with other extensions or custom code, temporary mitigations should include implementing strict Content Security Policy headers that restrict script execution sources and disable inline scripts where possible. Additionally, administrators should review access controls for the CentralNotice configuration interface to ensure only trusted users have write permissions. Input validation at both the client and server side is critical; while client-side checks provide user feedback, they are easily bypassed and must not be relied upon as a primary defense. Server-side sanitization using context-aware encoding functions that convert special characters into their HTML entity equivalents before rendering output in web pages remains the most effective technical control to prevent this class of vulnerability from being exploited.