# CVE-2026-55791

## Summary

- **CVE ID:** CVE-2026-55791
- **Severity:** MEDIUM
- **CVSS Score:** 6.9 (CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N)
- **CWE:** CWE-918, CWE-644, CWE-79
- **Published:** Jul 1, 2026
- **Last Modified:** Jul 2, 2026

## 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.

## Affected Products

- craftcms — cms (>= 5.0.0-RC1, < 5.10.0)
- craftcms — cms (>= 4.0.0-RC1, < 4.18.0)

## References

- [CNA](https://github.com/craftcms/cms/security/advisories/GHSA-c55v-343g-5xff)
- [CNA](https://github.com/craftcms/cms/pull/18559)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.46%
- **EPSS Percentile:** 38.8

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-12._