CVE-2021-40109

Severity: medium (CVSS 6.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-09-27 · updated 2026-06-17
Weakness: CWE-918

Description

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

Concrete CMS: before 8.5.6 — fixed in 8.5.6

How to fix

Upgrade to a fixed version: Concrete CMS 8.5.6. Check the vendor advisory for mitigations.

References

https://documentation.concretecms.org/developers/introduction/version-history/856-release-notes
https://hackerone.com/reports/1102105
https://documentation.concretecms.org/developers/introduction/version-history/856-release-notes
https://hackerone.com/reports/1102105

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