# CVE-2026-8238: Concrete CMS IDOR in conversation message endpoint

Source: https://junglewise.ai/threats/cve-2026-8238-concrete-cms-idor-in-conversation-message-endpoint  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-21. Updated: 2026-06-24  
License: CC BY 4.0 with a link back

CVE-2026-8238 · Severity: medium · CVSS 4 · Published 2026-05-21

Concrete CMS, a popular content management system, contains a security flaw in its conversation messaging system. An unauthorized person can view the full content of any conversation message on the site, including those from private or restricted areas. This could lead to the exposure of sensitive discussions and private file attachments.

Technologies: [Concrete CMS](https://junglewise.ai/threats/technologies/concrete-cms), [concrete5/concrete5 (Packagist)](https://junglewise.ai/threats/technologies/concrete5-concrete5). Vendors: [Concrete CMS](https://junglewise.ai/threats/vendors/concrete-cms), [Packagist](https://junglewise.ai/threats/vendors/packagist).

## Quick answers

**Is CVE-2026-8238 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-8238 being exploited in the wild.

**How severe is CVE-2026-8238?** Medium severity, with a CVSS score of 4, published 21 May 2026.

**Which products and versions are affected?** Concrete CMS <= 9.5.0, 9.5.0 and below; concrete5/concrete5 (Packagist) < 9.5.1, ECOSYSTEM:introduced=0,fixed=9.5.1.

**Is there a fix for CVE-2026-8238?** Yes. concrete5/concrete5 (Packagist): upgrade to 9.5.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-8238 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-8238?** Check whether you run Concrete CMS or concrete5/concrete5 (Packagist) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- concrete5/concrete5 (Packagist): upgrade to 9.5.1 or later

  ```sh
  composer require concrete5/concrete5:^9.5.1
  ```


## Technical details

An Insecure Direct Object Reference (IDOR) vulnerability exists in Concrete CMS versions 9.5.0 and below. The '/ccm/frontend/conversations/message_page' endpoint fails to implement proper authorization checks, allowing an unauthenticated attacker to enumerate and retrieve the full content of any conversation message by manipulating identifiers. This exposure includes messages from restricted pages, member-only areas, and the moderation queue, as well as file attachments with their associated download URLs. The vulnerability is addressed in version 9.5.1.

## Affected products

- Concrete CMS Concrete CMS <= 9.5.0

## Identifiers

- CVE-2026-8238
- GHSA-qv3x-mffx-9gw8

## Timeline

- 2026-05-21: disclosed: NVD published date
- 2026-05-22: advisory: GitHub Advisory published
- 2026-06-24: patched: Advisory updated with patch information for version 9.5.1

## References

- [https://documentation.concretecms.org/9-x/developers/introduction/version-history/951-release-notes](https://documentation.concretecms.org/9-x/developers/introduction/version-history/951-release-notes)

## Related threats

- [Concrete CMS OAuth REST API authorization bypass](https://junglewise.ai/threats/cve-2026-85387-concrete-cms-oauth-rest-api-authorization-bypass)
- [Concrete CMS unauthenticated Express entry search disclosure](https://junglewise.ai/threats/cve-2026-18120-concrete-cms-unauthenticated-express-entry-search-disclosure)
- [Concrete CMS REST API user creation permission bypass](https://junglewise.ai/threats/cve-2026-87031-concrete-cms-rest-api-user-creation-permission-bypass)
- [Concrete CMS access control bypass in board custom-slot preview](https://junglewise.ai/threats/cve-2026-87028-concrete-cms-access-control-bypass-in-board-custom-slot-preview)
- [Concrete CMS stored XSS via XML file upload in Form Block](https://junglewise.ai/threats/cve-2026-85386-concrete-cms-stored-xss-via-xml-file-upload-in-form-block)