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Advisory record · GHSA-c55v-343g-5xff

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

CVSS 6.9 MediumEPSS 0.0046 · 40th percentile

Published by the GitHub Advisory Database at 19 Jun 2026, 21:15 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
craftcms/cmsPackagist>=5.0.0-RC1, <5.10 || >=4.0.0-RC1, <4.185.10, 4.18
Identifiers
GHSA-c55v-343g-5xff · CVE-2026-55791 · PKSA-5xds-5mf3-ckxn
Weakness (CWE)
CWE-79 · CWE-346 · CWE-644 · CWE-918
Tags
Published
19 Jun 2026
Updated
10 Sept 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Craft CMS (craftcms/cms) versions from 4.0.0-RC1 to before 4.18, and from 5.0.0-RC1 to before 5.10, are affected through the resource JavaScript action, which can be made to fetch and return attacker-controlled content as JavaScript when a Host header is poisoned and assetManager.cacheSourcePaths is set to false. An unauthenticated attacker can send a crafted request to trigger server-side request forgery and arbitrary JavaScript injection, and the source says this can extend to cache poisoning when a caching layer is present. Upgrade to 4.18, 5.10, or a later release.

Written 31 Oct 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
6.9 Medium 4.0 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 CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0046, the 40th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 13:57 UTC First seen by agentprime
  2. 31 Oct 2026, 13:57 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.