# CVE-2026-7886: Concrete CMS 9.5.0 and below is vulnerable to IDOR in AddMessage/UpdateMessage via attachments[] parameter

> Attackers can bypass file permissions to read arbitrary files by manipulating attachment IDs in conversation messages.

- **Severity:** Low 2.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 21 May 2026
- **Updated:** 22 May 2026
- **Also known as:** GHSA-p8p9-5953-h9jw

## What is CVE-2026-7886?

CVE-2026-7886 is a low-severity missing authorization vulnerability in Concretecms Concrete Cms, published on 21 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Concrete CMS 9.5.0 and below is vulnerable to IDOR in AddMessage/UpdateMessage via attachments[] parameter which can lead to file permission bypass. The `AddMessage` and `UpdateMessage` conversation controllers accept user-supplied file attachment IDs and load files directly via `$em->find(File::class, $attachmentID)` without checking per-file permissions (`canViewFile()`). A user who can post in any conversation can reference any file in the CMS file manager by its sequential ID, effectively bypassing the file permission system.  The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 2.3 with a vector CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N. Thanks Tristan Mandani for reporting. if a site truly has private files, the owner should set up a  private storage location https://documentation.concretecms.org/user-guide/editors-reference/dashboard/system-and-maintenance/files/file-storage-locations  outside of the webroot so that permissions can be checked on view as well. That way, even if a authorized user attaches a file, or otherwise links to it, unauthorized users won't be able to view the file.

Weakness: CWE-639 (Authorization Bypass Through User-Controlled Key)

## Which versions are affected by CVE-2026-7886?

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-2026-7886?

Upgrade concrete5/concrete5 to 9.5.1 or later.

## Is CVE-2026-7886 being exploited?

There is no known exploitation of CVE-2026-7886 in the wild and no public exploit code.

## 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-2026-7886 and fix it if it is affected.

What it is: CVE-2026-7886 is a low-severity missing authorization vulnerability in Concretecms Concrete Cms, published on 21 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-7886 in the wild and no public exploit code.

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-2026-7886/ (Markdown: https://insights.sbomify.com/CVE-2026-7886/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-7886
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-7886
- OSV: https://osv.dev/vulnerability/CVE-2026-7886

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-7886/
Summaries are generated and may contain mistakes; the official description above is the record.