CVE-2026-55691: Starcitizenwiki/embedvideo Cross-Site Scripting Vulnerability

HIGH
Advisory Identifier: GHSA-7h5p-637f-jfr7
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CVSS 8.6
CWE-80 CWE-79
Published
Advisory Summary

CVE-2026-55691 is a HIGH (CVSS 8.6) cross-site scripting vulnerability (CWE-80: Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)) affecting Starcitizenwiki/embedvideo libraries in the Packagist ecosystem. The issue involves stored xss via unsanitized class passed to template. Remediation is available by upgrading affected packages to version 4.1.0.

CVE-2026-55691 at a Glance

CVE Identifier CVE-2026-55691
GHSA Identifier GHSA-7h5p-637f-jfr7
Severity HIGH
CVSS v3.1 Base Score 8.6
CWE Classification CWE-80: Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)
Affected Product Starcitizenwiki/embedvideo
Package Ecosystem Packagist
Published Date
Last Updated

Security Impact

CVSS: 8.6

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity Low (I:L)
Availability Low (A:L)

How to Fix CVE-2026-55691

To remediate this vulnerability, upgrade all affected Starcitizenwiki/embedvideo dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

starcitizenwiki/embedvideo fixed: 4.1.0 
Upgrade starcitizenwiki/embedvideo to 4.1.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for starcitizenwiki/embedvideo

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-55691, inspect your project dependencies for Starcitizenwiki/embedvideo:

inspect dependencies for starcitizenwiki/embedvideo

Analyze the terminal output to locate any version of Starcitizenwiki/embedvideo in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.1.0), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-80: Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS), where 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. In Starcitizenwiki/embedvideo, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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.

CVE-2026-55691 Affected Starcitizenwiki/embedvideo Versions

1 component(s)
Fixed Versions:
4.1.0
Product / Package Ecosystem Affected Versions Fixed Version
starcitizenwiki/embedvideo
 Packagist
< 4.1.0
4.1.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/StarCitizenWiki/mediawiki-extensions-EmbedVideo/security/advisories/GHSA-7h5p-637f-jfr7
Security Fix Commit FIX COMMIT
https://github.com/StarCitizenWiki/mediawiki-extensions-EmbedVideo/commit/370156335b325bb81d14d89edf0a1f2643d50a84
Starcitizenwiki/embedvideo Source Repository REPOSITORY
https://github.com/StarCitizenWiki/mediawiki-extensions-EmbedVideo
Starcitizenwiki/embedvideo Release RELEASE
https://github.com/StarCitizenWiki/mediawiki-extensions-EmbedVideo/releases/tag/v4.1.0

Frequently Asked Questions

What is CVE-2026-55691?
CVE-2026-55691 is a security vulnerability in Starcitizenwiki/embedvideo involving Stored XSS via unsanitized class passed to template under CWE-80: Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS).
Which Starcitizenwiki/embedvideo versions are affected?
Affected versions include releases prior to 4.1.0 across affected packages: starcitizenwiki/embedvideo.
What version fixes CVE-2026-55691?
Upgrading to 4.1.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is starcitizenwiki/embedvideo affected?
Yes, starcitizenwiki/embedvideo is affected in releases prior to 4.1.0. Upgrade your dependency to 4.1.0 or later.
What is the CVSS score of CVE-2026-55691?
CVE-2026-55691 has a CVSS v3.1 base score of 8.6 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L.
What CWE is associated with CVE-2026-55691?
CVE-2026-55691 is classified under CWE-80: 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.).
How can I check Packagist dependencies for CVE-2026-55691?
Run the dependency tree command: 'inspect dependencies for starcitizenwiki/embedvideo'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-7h5p-637f-jfr7",
  "modified" : "2026-06-19T21:15:03Z",
  "published" : "2026-06-19T21:15:03Z",
  "aliases" : [ "CVE-2026-55691" ],
  "summary" : "StarCitizenWiki Extension Embed Video: Stored XSS via unsanitized class passed to template",
  "details" : "### Summary\nThe 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.\n\n### Details\nThe 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.\n\n```\n$template = <<<HTML\n    <figure class=\"%s\" data-service=\"%s\" %s %s>\n        <div class=\"embedvideo-wrapper\" %s>%s%s%s</div>%s\n    </figure>\nHTML;\n```\n\n### PoC\nNote the double quote immediately following the single quote to escape the class attribute in the template:\n```\n<youtube class='\" onmouseover=\"alert(document.domain)' id=\"dQw4w9WgXcQ\">dQw4w9WgXcQ</youtube>\n```\n\n### Impact\nArbitrary HTML can be inserted into the DOM by any user on any page, allowing for JavaScript to be executed.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "starcitizenwiki/embedvideo"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.1.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.0.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/StarCitizenWiki/mediawiki-extensions-EmbedVideo/security/advisories/GHSA-7h5p-637f-jfr7"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/StarCitizenWiki/mediawiki-extensions-EmbedVideo/commit/370156335b325bb81d14d89edf0a1f2643d50a84"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/StarCitizenWiki/mediawiki-extensions-EmbedVideo"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/StarCitizenWiki/mediawiki-extensions-EmbedVideo/releases/tag/v4.1.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79", "CWE-80" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-19T21:15:03Z",
    "nvd_published_at" : null
  }
}