CVE-2026-55691
Published:June 19, 2026
Updated:June 21, 2026
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" (https://github.com/StarCitizenWiki/mediawiki-extensions-EmbedVideo/blob/a573a16d925ee0ea0d34b360856dc8ab0b88f822/includes/EmbedService/EmbedHtmlFormatter.php#L138) adds a figure with a class that is substituted in. This value is provided to sprintf "here" (https://github.com/StarCitizenWiki/mediawiki-extensions-EmbedVideo/blob/a573a16d925ee0ea0d34b360856dc8ab0b88f822/includes/EmbedService/EmbedHtmlFormatter.php#L156), 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.
Affected Packages
https://github.com/StarCitizenWiki/mediawiki-extensions-EmbedVideo.git (GITHUB):
Affected version(s) >=v1.0 <v4.1.0Fix Suggestion:
Update to version v4.1.0starcitizenwiki/embedvideo (PHP):
Affected version(s) >=dev-ci-js <4.1.0Fix Suggestion:
Update to version 4.1.0Related Resources (4)
Do you need more information?
Contact UsCVSS v4
Base Score:
8.8
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
HIGH
Vulnerable System Integrity
LOW
Vulnerable System Availability
LOW
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
8.6
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
LOW
Availability
LOW