# CVE-2026-82920: Mattermost ABAC parent policy bypass via policy update endpoint

> Channel or team administrators can bypass ABAC restrictions by detaching system-assigned parent policies via a crafted API request.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 14 Sep 2026
- **Updated:** 14 Sep 2026
- **Also known as:** GHSA-v87m-p66q-xcjg

## What is CVE-2026-82920?

CVE-2026-82920 is a medium-severity missing authorization vulnerability in Mattermost Mattermost Server, published on 14 Sep 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7 fail to enforce authorization boundaries on the access control policy update endpoint which allows a channel or team administrator to detach a system-assigned ABAC parent policy via a crafted PUT /api/v4/access_control_policies request with an empty imports list.. Mattermost Advisory ID: MMSA-2026-00724

Weakness: CWE-863 (Incorrect Authorization)

## Which versions are affected by CVE-2026-82920?

It affects 1 product.


Products: Mattermost Mattermost Server.

## How do I fix CVE-2026-82920?

No fix has been published for CVE-2026-82920 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-82920 being exploited?

There is no known exploitation of CVE-2026-82920 in the wild and no public exploit code.

## Other vulnerabilities in Mattermost Mattermost Server

- [CVE-2025-12419](https://insights.sbomify.com/CVE-2025-12419/): Account takeover on OAuth/OpenID-enabled servers (critical 9.9)
- [CVE-2025-12421](https://insights.sbomify.com/CVE-2025-12421/): Account Takeover via Code Exchange Endpoint (critical 9.9)
- [CVE-2025-4981](https://insights.sbomify.com/CVE-2025-4981/): Path Traversal Leading to RCE by Any Authenticated Mattermost User (critical 9.9)
- [CVE-2025-20051](https://insights.sbomify.com/CVE-2025-20051/): Arbitrary file read via block duplication in Mattermost Boards (critical 9.9)
- [CVE-2025-25279](https://insights.sbomify.com/CVE-2025-25279/): Arbitrary file read in Mattermost Boards via import & export board archive (critical 9.9)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-82920 and fix it if it is affected.

What it is: CVE-2026-82920 is a medium-severity missing authorization vulnerability in Mattermost Mattermost Server, published on 14 Sep 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-82920 in the wild and no public exploit code.

Affected product: Mattermost Mattermost Server. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-82920/ (Markdown: https://insights.sbomify.com/CVE-2026-82920/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-82920
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-82920
- OSV: https://osv.dev/vulnerability/CVE-2026-82920

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-82920/
Summaries are generated and may contain mistakes; the official description above is the record.