CVE-2026-100245 in MediaWiki
Summary
by MITRE • 09/29/2026
Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting') vulnerability in Wikimedia Foundation Mediawiki - Wikibase Extension allows Stored 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 • 09/30/2026
The vulnerability identified as Improper Neutralization of Input During Web Page Generation represents a critical security flaw within the Wikimedia Foundation's Mediawiki platform, specifically affecting the Wikibase Extension prior to versions 1.46.1, 1.45.5, and 1.43.10. This issue is classified under CWE-79, which denotes Cross-site Scripting (XSS), a widespread web security flaw that occurs when an application includes untrusted data in a new web page without proper validation or escaping. In the context of this specific extension, the vulnerability manifests as Stored XSS, meaning that malicious scripts are permanently stored on the target servers, typically within database entries such as wiki pages, comments, or metadata fields managed by Wikibase. Unlike reflected XSS where the attack payload is contained in a single request, stored XSS ensures that every user who views the affected content will have their browser execute the injected script, thereby amplifying the potential impact significantly across the platform's user base.
From a technical perspective, the flaw arises because the application fails to adequately sanitize or encode special characters within input fields before rendering them in HTML context. When an attacker submits data containing executable JavaScript code through any interface exposed by the Wikibase Extension that is not properly validated, this script becomes part of the stored content on the server. Subsequently, when other users access pages containing this malicious payload, their browsers interpret and execute the script as if it were legitimate page content. This bypasses same-origin policy protections because the code runs in the context of the trusted domain hosting the Mediawiki instance. The lack of robust output encoding allows attributes such as event handlers or script tags to be injected directly into the DOM structure, enabling arbitrary command execution within the user's browser environment.
The operational impact of this vulnerability is severe due to its stored nature and the high-trust context in which it operates on Wikimedia projects. Attackers can exploit this flaw to steal session cookies, hijack administrative accounts, or perform actions on behalf of victims without their knowledge. For instance, an attacker could craft a payload that exfiltrates sensitive data from active sessions to an external server controlled by the adversary. Furthermore, since Wikibase is often used for managing structured data and complex metadata in large-scale wiki environments, compromising user sessions can lead to unauthorized modifications of critical information or defacement of public-facing pages. The persistence of the malicious script means that even after the initial attack vector is identified, all subsequent visitors remain at risk until the vulnerable content is manually removed or patched, creating a prolonged window of exposure for the entire community using these versions of the extension.
Mitigation strategies must prioritize immediate patching and rigorous input validation practices. The primary remediation step is to upgrade the Mediawiki installation along with the Wikibase Extension to version 1.46.1, 1.45.5, or 1.43.10 or later, where these specific encoding flaws have been addressed by the developers. In environments where immediate patching is not feasible due to operational constraints, administrators should implement strict Content Security Policy headers that restrict script execution sources and disable inline scripts whenever possible. Additionally, deploying a Web Application Firewall can provide an additional layer of defense by filtering out requests containing known XSS patterns before they reach the application logic. Long-term resilience requires adopting secure coding standards such as OWASP Top Ten guidelines, ensuring that all user inputs are treated as untrusted data until explicitly validated and encoded for their specific output context, thereby neutralizing potential injection vectors at the source.
This vulnerability aligns with MITRE ATT&CK technique T1059, specifically sub-technique 007 which covers JavaScript execution in web browsers. The attack lifecycle involves initial access through a trusted interface, persistence via stored payload delivery, and credential access or data exfiltration upon victim interaction. Understanding this mapping helps security teams anticipate similar behaviors in other extensions or modules that handle user-generated content. By recognizing the pattern of improper neutralization during web page generation, organizations can better audit their codebases for similar weaknesses across different components of their infrastructure. Continuous monitoring and regular security assessments are essential to maintain integrity against evolving XSS tactics that continue to pose significant risks to dynamic web applications relying on rich text input and complex data structures like those found in Wikibase implementations.