CVE-2026-55691 is a high-severity (CVSS 8.6) vulnerability in starcitizenwiki/embedvideo. O3 Security confirms whether CVE-2026-55691 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
StarCitizenWiki Extension Embed Video: Stored XSS via unsanitized class passed to template
Real-World Exposure
starcitizenwiki/embedvideoReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | starcitizenwiki/embedvideo | all versions | 4.1.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for starcitizenwiki/embedvideo. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update starcitizenwiki/embedvideo to 4.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55691 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-55691 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-55691. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-55691 in your dependencies?
O3 detects CVE-2026-55691 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.