CVE-2026-8238: Concrete CMS is vulnerable to IDOR

May 22, 2026 (updated June 24, 2026)

Concrete CMS 9.5.0 and below is vulnerable to IDOR. The ‘/ccm/frontend/conversations/message_page’ endpoint returns the full content of any conversation message. An unauthenticated attacker can enumerate all conversation messages, including messages from restricted pages, member-only areas, and the moderation queue. File attachments with download URLs are also exposed.

References

documentation.concretecms.org/9-x/developers/introduction/version-history/951-release-notes
github.com/advisories/GHSA-qv3x-mffx-9gw8
nvd.nist.gov/vuln/detail/CVE-2026-8238

Code Behaviors & Features

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