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craftcms/cms · Security

Craft CMS: Authenticated "assets/preview-thumb" discloses signed fallback transform preview link to CP users without asset-view permission

GHSA ID
GHSA-x76w-8c62-48mg
CVE ID
CVE-2026-56384
Severity
medium
Published
Updated
CVSS v4
5.3 · 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

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

CWEs

  • CWE-200 · Exposure of Sensitive Information to an Unauthorized Actor
  • CWE-862 · Missing Authorization

References

Open GitHub