CVE-2026-56384
Craft CMS: Authenticated "assets/preview-thumb" discloses signed fallback transform preview link to CP users without asset-view permission
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: 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
How to fix CVE-2026-56384
To remediate CVE-2026-56384, upgrade the affected package to a fixed version below.
- —upgrade to 4.17.8 or later
Is CVE-2026-56384 being exploited?
Low — EPSS is 0.2%, meaning exploitation activity has not been observed at scale.
Affected packages (1)
- >= 4.0.0-RC1, < 4.17.8
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N |