GHSA-x76w-8c62-48mg
Craft CMS: Authenticated "assets/preview-thumb" discloses signed fallback transform preview link to CP users without asset-view permission
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
Summary
A user with Control Panel access but without permission to view a target private asset can call assets/preview-thumb and receive preview HTML that contains a signed fallback transform link for that private asset.
Details
Root-cause analysis:
- The endpoint accepts an attacker-controlled
assetId. - Asset is resolved, and thumbnail HTML is returned.
- No explicit asset-view permission check is performed before preview generation.
Impact
Type:
- Missing authorization
- Unauthorized preview-link disclosure
Affected deployments:
- Craft sites with control panel users who have partial permissions and private assets.
Security consequence:
- A control panel user without asset-view permission can still obtain signed preview transform link data for private assets.
- This may increase private asset exposure risk depending on deployment and endpoint chaining.
Resources
https://github.com/craftcms/cms/commit/d30df3112220db1ffd6726a3ed11857014c7fb27
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 GHSA-x76w-8c62-48mg 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 GHSA-x76w-8c62-48mg 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 GHSA-x76w-8c62-48mg. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-x76w-8c62-48mg in your dependencies?
O3 detects GHSA-x76w-8c62-48mg across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.