CVE-2026-55791: craftcms cms Cross-site Scripting

Vulnerability summary

CVE-2026-55791 is a medium (CVSS 6.9) Cross-site Scripting vulnerability in craftcms cms. EPSS estimates a 0.46% chance of exploitation in the next 30 days, higher than 38.8% of scored vulnerabilities.

Timeline

1. 01-07-2026
   PublishedVulnerability first disclosed.
2. 02-07-2026
   Last modifiedVulnerability information updated.

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.

• CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
• CWE-644Improper Neutralization of HTTP Headers for Scripting SyntaxThe product does not neutralize or incorrectly neutralizes web scripting syntax in HTTP headers that can be used by web browser components that can process raw headers, such as Flash.
• CWE-918Server-Side Request Forgery (SSRF)The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.