# CVE-2026-8237: Concrete CMS 9.5.0 and below is vulnerable to IDOR in the`/ccm/frontend/conversations/message_detail` endpoint

> Unauthenticated attackers can access private conversation messages and attachments via an IDOR vulnerability in Concrete CMS.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 21 May 2026
- **Updated:** 22 May 2026
- **Also known as:** GHSA-xpgc-7vc2-8725

## What is CVE-2026-8237?

CVE-2026-8237 is a medium-severity missing authorization vulnerability in Concretecms Concrete Cms, published on 21 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Concrete CMS 9.5.0 and below is vulnerable to IDOR. The `/ccm/frontend/conversations/message_detail` 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. The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 6.3 with Vector CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N. Thanks Eldudareeno for reporting.

Weakness: CWE-862 (Missing Authorization)

## Which versions are affected by CVE-2026-8237?

2 open source packages ship an affected version, including concrete5/concrete5. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `concrete5/concrete5` | Packagist | All versions | 9.5.1 |
| `concrete5/concrete5` | Packagist | All versions | 9.5.1 |

Products: Concretecms Concrete Cms.

## How do I fix CVE-2026-8237?

Upgrade concrete5/concrete5 to 9.5.1 or later.

## Is CVE-2026-8237 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-8237 exists.

Public exploit code:

- CVE-2026-8237 is an Insecure Direct Object Reference (IDOR) vulnerability caused by missing authorization checks in Concrete CMS 9.5.0 and earlier. (github_poc): https://github.com/aj2108/CVE-2026-8237
- Concrete CMS <= 9.5.0 - Unauthenticated Conversation Message Disclosure (IDOR) (nuclei): http/cves/2026/CVE-2026-8237.yaml

## Other vulnerabilities in Concretecms Concrete Cms

- [CVE-2023-48648](https://insights.sbomify.com/CVE-2023-48648/): Concrete CMS allows unauthorized access because directories can be created with insecure permissions (critical 9.8)
- [CVE-2022-21829](https://insights.sbomify.com/CVE-2022-21829/): Code injection in concrete CMS (critical 9.8)
- [CVE-2021-22958](https://insights.sbomify.com/CVE-2021-22958/): Server-Side Request Forgery vulnerability in concrete5 (critical 9.8)
- [CVE-2021-40098](https://insights.sbomify.com/CVE-2021-40098/): Path traversal in n/a (critical 9.8)
- [CVE-2026-8134](https://insights.sbomify.com/CVE-2026-8134/): Concrete CMS Vulnerable to Relative Path Traversal (critical 9.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-8237 and fix it if it is affected.

What it is: CVE-2026-8237 is a medium-severity missing authorization vulnerability in Concretecms Concrete Cms, published on 21 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-8237 exists.

Affected packages and fixed versions:
- concrete5/concrete5 (Packagist): affected all versions; fixed in 9.5.1
- concrete5/concrete5 (Packagist): affected all versions; fixed in 9.5.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-8237/ (Markdown: https://insights.sbomify.com/CVE-2026-8237/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-8237
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-8237
- OSV: https://osv.dev/vulnerability/CVE-2026-8237

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-8237/
Summaries are generated and may contain mistakes; the official description above is the record.