In short
- CVE-2026-56384 is a MEDIUM (CVSS 4.3) vulnerability affecting craftcms/cms.
- Chance of exploitation in the next 30 days (EPSS): 0.33%, higher than 26.3% of all vulnerabilities.
- Fix: update to 4.17.8, 5.9.14 or later.
| Package | Affected versions | Patched versions |
|---|
| craftcms/cms Packagist | ≥ 4.0.0-RC1, < 4.17.8≥ 5.0.0-RC1, < 5.9.14
| 4.17.85.9.14
|
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
NVD 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.
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