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CVE-2026-56384: Craft CMS - Missing Authorization in assets/preview-thumb Endpoint

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-06-21 · updated 2026-10-25
• Weakness: CWE-862

Description

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.

Affected products

• craftcms cms: from 4.0.0-RC1 before 4.17.8; from 5.0.0-RC1 before 5.9.14 — fixed in 4.17.8, 5.9.14

How to fix

Upgrade to a fixed version: craftcms cms 4.17.8, 5.9.14. Check the vendor advisory for mitigations.

References

• https://github.com/craftcms/cms/commit/d30df3112220db1ffd6726a3ed11857014c7fb27
• https://github.com/craftcms/cms/security/advisories/GHSA-x76w-8c62-48mg
• https://www.vulncheck.com/advisories/craft-cms-missing-authorization-in-assets-preview-thumb-endpoint

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