CVE-2026-56384
Craft CMS - Missing Authorization in assets/preview-thumb Endpoint
Blast Radius
craftcms/cms🐘craftcms/cmsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
Craft CMS contains a missing authorization vulnerability in the assets/preview-thumb endpoint. A Control Panel user without permission to view a target private asset can call the endpoint with an attacker-controlled assetId and receive preview HTML containing a signed fallback transform preview link for that private asset, because no asset-view permission check is performed before preview generation. This affects versions >= 4.0.0-RC1, <= 4.17.7 and >= 5.0.0-RC1, <= 5.9.13, and is fixed in 4.17.8 and 5.9.14.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | craftcms/cms | ≥ 4.0.0-RC1&&< 4.17.8 | 4.17.8 |
| 🐘Packagist | craftcms/cms | ≥ 5.0.0-RC1&&< 5.9.14 | 5.9.14 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for craftcms/cms. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update craftcms/cms to 4.17.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-56384 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-56384 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-56384. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-56384 in your dependencies?
O3 detects CVE-2026-56384 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.