Vulnerability · Published Jul 1, 2026 · Assigned by GitHub_M
CVE-2026-55791Craft CMS: Blind SSRF and Arbitrary JavaScript Injection via Host Header Poisoning in actionResourceJs
Medium 6.9
In plain English
A medium-severity server-side request forgery in cms from craftcms. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 40% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Packagist | craftcms/cms | 5.10 | GHSA-c55v-343g-5xff |
| Packagist | craftcms/cms | 4.18 | GHSA-c55v-343g-5xff |
Affected products (as reported)
Weakness: CWE-918, CWE-644, CWE-79 · Vector: 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
References
- https://github.com/craftcms/cms/security/advisories/GHSA-c55v-343g-5xff x_refsource_CONFIRM
- https://github.com/craftcms/cms/pull/18559 x_refsource_MISC