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StarCitizenWiki Extension Embed Video: Stored XSS via unsanitized class passed to template

High severity GitHub Reviewed Published Jun 19, 2026 in StarCitizenWiki/mediawiki-extensions-EmbedVideo • Updated Jun 19, 2026

Package

composer starcitizenwiki/embedvideo (Composer)

Affected versions

<= 4.0.0

Patched versions

4.1.0

Description

Summary

The user supplied class value is fed directly into the sprintf call that creates HTML. You can add a quote to escape the class and then inject arbitrary html/javascript to the final output.

Details

The template here adds a figure with a class that is substituted in. This value is provided to sprintf here, an unescaped version of the class supplied by the user.

$template = <<<HTML
    <figure class="%s" data-service="%s" %s %s>
        <div class="embedvideo-wrapper" %s>%s%s%s</div>%s
    </figure>
HTML;

PoC

Note the double quote immediately following the single quote to escape the class attribute in the template:

<youtube class='" onmouseover="alert(document.domain)' id="dQw4w9WgXcQ">dQw4w9WgXcQ</youtube>

Impact

Arbitrary HTML can be inserted into the DOM by any user on any page, allowing for JavaScript to be executed.

References

@octfx octfx published to StarCitizenWiki/mediawiki-extensions-EmbedVideo Jun 19, 2026
Published to the GitHub Advisory Database Jun 19, 2026
Reviewed Jun 19, 2026
Last updated Jun 19, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
Low
Availability
Low

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L

EPSS score

Weaknesses

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

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. Learn more on MITRE.

Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)

The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special characters such as <, >, and & that could be interpreted as web-scripting elements when they are sent to a downstream component that processes web pages. Learn more on MITRE.

CVE ID

CVE-2026-55691

GHSA ID

GHSA-7h5p-637f-jfr7

Source code

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