Vulnerability Description
Craft CMS is a content management system (CMS). Versions 4.0.0-RC1 and above, prior to 4.18.0 and 5.0.0-RC1, and above, prior to 5.10.0, are vulnerable to Server-Side Request Forgery (SSRF) and Arbitrary JavaScript Injection through the /actions/app/resource-js endpoint. By exploiting the default permissive trustedHosts configuration, an attacker can poison the Host or X-Forwarded-Host header to manipulate the application’s $baseUrl. This bypasses the endpoint’s internal URL validation, forcing the backend Guzzle client to fetch a malicious payload from an attacker-controlled server and reflect it to the client with a Content-Type: application/javascript header. The vulnerability manifests when assetManager.cacheSourcePaths is set to false. This issue has been fixed in versions 4.18.0 and 5.10.0.
Related Weaknesses (CWE)
References
- https://github.com/craftcms/cms/pull/18559
- https://github.com/craftcms/cms/security/advisories/GHSA-c55v-343g-5xff
FAQ
What is CVE-2026-55791?
CVE-2026-55791 is a documented vulnerability. Craft CMS is a content management system (CMS). Versions 4.0.0-RC1 and above, prior to 4.18.0 and 5.0.0-RC1, and above, prior to 5.10.0, are vulnerable to Server-Side Request Forgery (SSRF) and Arbitr...
How severe is CVE-2026-55791?
CVSS scoring is not yet available for CVE-2026-55791. Check NVD for updates.
Is there a patch for CVE-2026-55791?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.