Craft CMS previewthumb auth bypass pre 4.17.8/5.9.14
CVE-2026-56384 Published on June 21, 2026
Craft CMS - Missing Authorization in assets/preview-thumb Endpoint
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.
Vulnerability Analysis
CVE-2026-56384 is exploitable with network access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have a small impact on confidentiality, a small impact on integrity and availability.
Weakness Type
What is an AuthZ Vulnerability?
The software does not perform an authorization check when an actor attempts to access a resource or perform an action.
CVE-2026-56384 has been classified to as an AuthZ vulnerability or weakness.
Products Associated with CVE-2026-56384
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Affected Versions
craftcms cms:- Version 4.0.0-RC1 and below 4.17.8 is affected.
- Version 4.17.8 is unaffected.
- Version 5.0.0-RC1 and below 5.9.14 is affected.
- Version 5.9.14 is unaffected.