CVE-2026-55691 EmbedVideo Extension : Stored XSS via unsanitized class passed to template
A stored XSS vulnerability in the EmbedVideo MediaWiki extension allows attackers to inject malicious scripts via unsanitized class attributes, affecting wiki visitors.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-55691?
CVE-2026-55691 is a high-severity cross-site scripting vulnerability in StarCitizenWiki mediawiki-extensions-EmbedVideo, published on 15 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-79
Which versions are affected by CVE-2026-55691?
2 open source packages ship an affected version, including starcitizenwiki/embedvideo.
| Package | Affected | Fixed in |
|---|---|---|
starcitizenwiki/embedvideo Packagist | All versions | 4.1.0 |
starcitizenwiki/embedvideo Packagist | All versions | 4.1.0 |
How do I fix CVE-2026-55691?
Upgrade starcitizenwiki/embedvideo to 4.1.0 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-55691 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55691 exists.
Sources
Also known as GHSA-7h5p-637f-jfr7.