# CVE-2026-8239: Concrete CMS IDOR in conversation rating endpoint

Source: https://junglewise.ai/threats/cve-2026-8239-concrete-cms-idor-in-conversation-rating-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-2026-8239 · Severity: medium · CVSS 4 · Published 2026-05-21

Concrete CMS, a popular content management system, contains a security flaw that allows unauthorized users to view information about private messages. By manipulating message identifiers, an attacker can confirm if a specific message exists and view its rating score. This could lead to the exposure of metadata about private communications within the platform.

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-2026-8239 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-8239 being exploited in the wild.

**How severe is CVE-2026-8239?** 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-2026-8239?** 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-2026-8239 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-8239?** 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 due to missing authorization checks in the '/ccm/frontend/conversations/get_rating' endpoint. An unauthenticated attacker can send network requests to this endpoint with arbitrary message IDs to confirm the existence of messages and retrieve their associated rating scores. This occurs because the application fails to verify if the requester has the appropriate permissions to access the metadata of the specified message object. The issue is addressed in version 9.5.1.

## Affected products

- Concrete CMS Concrete CMS <= 9.5.0

## Identifiers

- CVE-2026-8239
- GHSA-2xp7-rpvc-pjwc

## Timeline

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

## 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)