CVE-2026-100380 in MediaWiki
Summary
by MITRE • 09/25/2026
Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting') vulnerability in Wikimedia Foundation Mediawiki - Wikibase Extension allows Cross-Site Scripting (XSS).
This issue affects Mediawiki - Wikibase Extension: from * before 1.46.1, 1.45.5, 1.43.10.
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Analysis
by VulDB Data Team • 09/25/2026
The Wikimedia Foundation's MediaWiki platform, specifically through its Wikibase extension, has been identified with a critical security flaw classified as an Improper Neutralization of Input During Web Page Generation vulnerability. This issue manifests as a Cross-Site Scripting (XSS) attack vector that allows malicious actors to inject executable scripts into web pages viewed by other users. The vulnerability affects multiple versions of the MediaWiki Wikibase extension, including those prior to version 1.46.1, version 1.45.5, and version 1.43.10. This widespread impact across several major release branches underscores a systemic issue in how user-supplied data is processed and rendered within the application's interface components related to Wikibase functionality.
At its core, this vulnerability stems from insufficient validation or encoding of input data before it is included in dynamically generated HTML content. When an attacker crafts a malicious payload containing JavaScript code and submits it through any vulnerable input field associated with the Wikibase extension, the server fails to properly sanitize the entry. Consequently, when another user accesses the affected page, their browser interprets the injected script as legitimate content from the trusted domain. This bypasses standard security mechanisms such as the Same-Origin Policy, enabling the attacker's code to execute within the context of the victim's session. The technical flaw aligns directly with CWE-79, which defines Improper Neutralization of Input During Web Page Generation (XSS), highlighting a failure in input validation and output encoding practices essential for web application security.
The operational impact of this vulnerability is severe due to its potential for widespread exploitation within collaborative knowledge platforms like Wikipedia or internal enterprise wikis powered by MediaWiki. Successful exploitation allows attackers to perform actions on behalf of the victim, including stealing session cookies, hijacking user sessions, and performing unauthorized administrative actions if the targeted user has elevated privileges. Furthermore, XSS attacks can be used to deface web pages, redirect users to malicious sites designed for phishing or malware distribution, and harvest sensitive information such as personal data or internal documentation stored within the wiki environment. In collaborative environments where trust among contributors is paramount, this breach of integrity can lead to significant reputational damage and loss of confidence in the platform's security posture.
From a tactical perspective, this vulnerability maps to several techniques within the MITRE ATT&CK framework for web applications. It primarily corresponds to T1059, Command and Scripting Interpreter, specifically through client-side scripting languages like JavaScript. Additionally, it relates to T1204, User Execution, as it relies on tricking a user into visiting a maliciously crafted page or link that triggers the script execution in their browser. The attack chain often involves social engineering elements where an attacker might embed the payload in a seemingly innocuous edit suggestion, talk page comment, or metadata field within Wikibase entities to increase the likelihood of interaction by other users.
Mitigation strategies must focus on immediate patching and robust input handling practices. Administrators running affected versions should upgrade their MediaWiki installation along with the Wikibase extension to version 1.46.1, 1.45.5, or 1.43.10 respectively, as these releases contain specific fixes for this sanitization issue. For organizations unable to patch immediately due to compatibility constraints, implementing a Web Application Firewall (WAF) with rules designed to detect and block common XSS payloads can provide temporary protection by filtering malicious input at the network perimeter. Developers should also review any custom extensions or skins that interact with Wikibase data to ensure they adhere to strict output encoding standards using libraries such as HTMLPurifier, which is commonly integrated into MediaWiki but may require configuration updates for newer attack vectors.
Long-term remediation requires a shift in development methodology toward secure coding practices that prioritize defense-in-depth. This includes enforcing Content Security Policy (CSP) headers to restrict the sources from which scripts can be loaded and executed, thereby mitigating the impact of any successful XSS injection even if input validation fails. Regular security audits and penetration testing focused on web application vulnerabilities are essential to identify similar flaws in other components of the MediaWiki ecosystem. By addressing both the immediate technical flaw and strengthening overall architectural controls against client-side code injection, organizations can significantly reduce their risk exposure and maintain the integrity of their collaborative knowledge bases.