CVE-2026-103584 in MediaWiki
Summary
by MITRE • 10/01/2026
Improper neutralization of Script-Related HTML tags in a web page (basic XSS) vulnerability in The Wikimedia Foundation MediaWiki CommonsMetadata extension allows Cross-Site Scripting (XSS).
This issue affects MediaWiki CommonsMetadata extension: 1.46, 1.45, and 1.43.
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Analysis
by VulDB Data Team • 10/01/2026
The identified vulnerability represents a classic instance of improper neutralization of script-related HTML tags within web pages, commonly categorized as basic Cross-Site Scripting or XSS. This flaw resides specifically in the Wikimedia Foundation MediaWiki CommonsMetadata extension for versions 1.46, 1.45, and 1.43. The core technical failure involves the application's inability to properly sanitize user-supplied input before rendering it within an HTML context. When a web page fails to neutralize special characters that have script-related meanings, such as angle brackets or quotation marks, malicious actors can inject executable JavaScript code into the victim's browser session. This occurs because the extension does not adequately validate or encode metadata fields that are subsequently displayed on public-facing pages, allowing raw HTML and script tags to pass through the filtering mechanisms intact.
From a technical perspective, this vulnerability aligns with CWE-79, which defines Improper Neutralization of Input During Web Page Generation. The absence of robust output encoding means that any user-controlled data processed by the CommonsMetadata extension can be interpreted as executable code rather than inert text. An attacker could craft a malicious payload containing JavaScript snippets embedded within metadata fields associated with uploaded images or other media assets. When another user views this content, their browser executes the injected script in the context of the vulnerable website. This execution environment grants the malicious script access to cookies, session tokens, and potentially sensitive page data that would otherwise be restricted by same-origin policies if the code were properly neutralized.
The operational impact of this vulnerability is significant for both individual users and the broader Wikimedia infrastructure. Successful exploitation allows an attacker to perform actions on behalf of a victim user without their knowledge or consent. This can include stealing session cookies to hijack accounts, defacing web pages by altering displayed content, redirecting users to phishing sites designed to harvest credentials, or harvesting sensitive information such as personal identifiers and browsing history stored in local storage. In the context of Wikimedia projects, where community trust and data integrity are paramount, even a basic XSS vulnerability can erode user confidence and compromise the security posture of collaborative platforms that rely on open contribution models.
Mitigation strategies must focus on immediate remediation through software updates and long-term architectural improvements. The most effective solution is to upgrade the MediaWiki CommonsMetadata extension to a patched version where this input validation issue has been resolved by developers who have implemented strict output encoding for all metadata fields displayed in HTML contexts. Administrators should verify their current extension versions against the affected list of 1.46, 1.45, and 1.43 and apply updates promptly. Additionally, implementing Content Security Policy headers can provide a layer of defense-in-depth by restricting the sources from which scripts are allowed to execute, thereby mitigating the impact even if an XSS vector is discovered in other parts of the application.
From a threat intelligence perspective, this vulnerability maps directly to MITRE ATT&CK technique T1059.007, specifically JavaScript execution within browser environments. Attackers frequently leverage such flaws during reconnaissance and initial access phases to establish persistence or escalate privileges through client-side attacks. Understanding this mapping helps security teams prioritize patching efforts based on the potential for exploitation in real-world attack chains. Continuous monitoring of web application firewalls for patterns indicative of script injection can also aid in detecting attempted exploits before they succeed, providing an additional layer of protection while infrastructure updates are being deployed across Wikimedia's distributed systems.