CVE-2021-40109: Concretecms Concrete CMS

Medium severity, CVSS 6.4. EPSS: 0.5% chance of exploitation in the next 30 days.

A SSRF issue was discovered in Concrete CMS through 8.5.5. Users can access forbidden files on their local network. A user with permissions to upload files from external sites can upload a URL that redirects to an internal resource of any file type. The redirect is followed and loads the contents of the file from the redirected-to server. Files of disallowed types can be uploaded.

Affected products

• Concretecms Concrete CMS: before 8.5.6 (fixed in 8.5.6)

Published 2021-09-27. Last modified 2026-06-17.