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EUVD-2026-329891

2026-10-16T14:13:51.302233+00:00

EUVD-2026-329891

fkie_cve-2026-56384

2026-10-16T14:13:51.302279+00:00

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.

GHSA-x76w-8c62-48mg — Craft CMS: Authenticated "assets/preview-thumb" discloses signed fallback transform preview link to CP users without as…

2026-10-16T14:13:51.302313+00:00

Affected: Packagist: craftcms/cms

### 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: 1. The endpoint accepts an attacker-controlled `assetId`. 2. Asset is resolved, and thumbnail HTML is returned. 3. No explicit asset-view permission check is performed before preview generation.

### Impact

Type:

1. Missing authorization 2. Unauthorized preview-link disclosure

Affected deployments:

1. Craft sites with control panel users who have partial permissions and private assets.

Security consequence:

1. A control panel user without asset-view permission can still obtain signed preview transform link data for private assets. 2. This may increase private asset exposure risk depending on deployment and endpoint chaining.

## Resources

https://github.com/craftcms/cms/commit/d30df3112220db1ffd6726a3ed11857014c7fb27