# [CRIT] [GHSA / CRITICAL] CVE-2026-55791: Craft CMS: Blind SSRF and Arbitrary JavaScript Injection via Host Header Poisoning in actionResourceJs

**Source:** GitHub Security Advisories
**Published:** 2026-06-19
**Article:** https://github.com/advisories/GHSA-c55v-343g-5xff

## Threat Profile

Craft CMS: Blind SSRF and Arbitrary JavaScript Injection via Host Header Poisoning in actionResourceJs

**1. Overview**

Craft CMS is 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, forci…

## Indicators of Compromise (high-fidelity only)

- **CVE:** `CVE-2026-55791`

## MITRE ATT&CK Techniques

- **T1190** — Exploit Public-Facing Application

## Kill chain phases observed

_(none detected from narrative keywords)_

## Recommended hunts

### IOC-driven hunts (use shared templates)

These are standard IOC-substitution hunts — the canonical SPL and KQL live once in [`_TEMPLATES.md`](../_TEMPLATES.md), so we don't repeat the same boilerplate on every CVE / hash / network-IOC briefing.

- **Asset exposure — vulnerability matches article CVE(s)** ([template](../_TEMPLATES.md#asset-exposure)) — phase: **recon**, confidence: **High**
  - CVE(s): `CVE-2026-55791`


## Why this matters

Severity classified as **CRIT** based on: CVE present, 1 use case(s) fired, 1 technique(s) inferred. Read the full article for actor attribution, tooling details, and any defanged IOCs in the body that aren't visible in the RSS summary.