CVE-2026-55691
Received Received - Intake

EmbedVideo Extension HTML Attribute Injection Vulnerability

Publication date: 2026-09-15

Last updated on: 2026-09-15

Assigner: GitHub, Inc.

Description
The EmbedVideo Extension is a MediaWiki extension which adds a parser function called #ev and various parser tags for embedding video clips from various video sharing services. Prior to 4.1.0, EmbedHtmlFormatter::toHtml in includes/EmbedService/EmbedHtmlFormatter.php passes the user-supplied class value directly to sprintf while constructing a figure element. A quote in the class value can terminate the class attribute and inject arbitrary HTML attributes or markup into the rendered page. A user able to edit a wiki page can store JavaScript that executes for visitors who render the affected content. This issue is fixed in version 4.1.0.

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Meta Information

Published
2026-09-15
Last Modified
2026-09-15
Generated
2026-09-15
AI Q&A
2026-09-15
EPSS Evaluated
N/A
NVD
CVE-2026-55691
EUVD
EUVD-2026-78832

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
mediawiki embedvideo_extension to 4.1.0 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-79 The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

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Executive Summary

CVE-2026-55691 is a Stored Cross-Site Scripting (XSS) vulnerability in the MediaWiki EmbedVideo extension. It occurs when user-supplied class values are directly inserted into HTML templates without proper sanitization. An attacker can inject malicious HTML or JavaScript by escaping the class attribute, allowing arbitrary script execution in the browsers of users viewing the affected page.

Detection Guidance

To detect this vulnerability, check the version of the EmbedVideo extension installed on your MediaWiki system. If the version is 4.0.0 or lower, the system is vulnerable. Run the following command to check the version: grep -r "EmbedVideo" /path/to/mediawiki/extensions/ | grep "version"

Impact Analysis

This vulnerability allows an attacker with edit access to a wiki page to inject malicious scripts. When other users view the page, the injected scripts execute in their browsers, potentially stealing session cookies, redirecting to phishing sites, or performing actions on their behalf. No privileges or user interaction are required for the attack.

Compliance Impact

This vulnerability could lead to unauthorized access to user data, violating GDPR's data protection requirements and HIPAA's safeguards for protected health information. A successful exploit may result in data breaches, triggering compliance violations and potential legal penalties.

Mitigation Strategies

Immediately update the EmbedVideo extension to version 4.1.0 or later. If updating is not possible, apply the patch from commit 370156335b325bb81d14d89edf0a1f2643d50a84. Disable the extension temporarily if an update is not feasible.

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