GitHub Advisoryadvisory · Packagist

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

MEDIUM Published 2026-07-06 Modified 2026-08-06 Official page ↗
Aliases
CVE-2026-56384
Ecosystem
Packagist
Packages
craftcms/cms
Severity
Moderate
CVSS vector
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
Weaknesses
CWE-200, CWE-862
Reviewed
2026-07-06

Affected packages

• Packagist craftcms/cms: >= 4.0.0-RC1, < 4.17.8 → fixed in 4.17.8 • Packagist craftcms/cms: >= 5.0.0-RC1, < 5.9.14 → fixed in 5.9.14

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: 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

Related

Alias · CVE (1)

  • CVE-2026-56384 Craft CMS contains a missing authorization vulnerability in the assets/preview-thumb endpoint. vulnerability

Weakness · CWE (2)

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

References