# CVE-2026-3524: Authorization Bypass in Mattermost Legal Hold Plugin Due to Missing Return After Permission Check

> An authenticated attacker can bypass authorization checks to access, create, download, and delete legal hold data in the Mattermost Legal Hold Plugin.

- **Severity:** High 8.3 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 6 Apr 2026
- **Updated:** 7 Apr 2026
- **Also known as:** GHSA-h7g6-pq3g-f7cw

## What is CVE-2026-3524?

CVE-2026-3524 is a high-severity missing authorization vulnerability in Mattermost, published on 6 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Mattermost Plugin Legal Hold versions <=1.1.4 fail to halt request processing after a failed authorization check in ServeHTTP which allows an authenticated attacker to access, create, download, and delete legal hold data via crafted API requests to the plugin's endpoints. Mattermost Advisory ID: MMSA-2026-00621

Weakness: CWE-862 (Missing Authorization)

## Which versions are affected by CVE-2026-3524?

It affects 1 product.


Products: Mattermost Legal Hold.

## How do I fix CVE-2026-3524?

No fix has been published for CVE-2026-3524 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-3524 being exploited?

There is no known exploitation of CVE-2026-3524 in the wild and no public exploit code.

## Other vulnerabilities in Mattermost

- [CVE-2026-6957](https://insights.sbomify.com/CVE-2026-6957/): Path traversal in Mattermost (high 8.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-3524 and fix it if it is affected.

What it is: CVE-2026-3524 is a high-severity missing authorization vulnerability in Mattermost, published on 6 Apr 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-2026-3524 in the wild and no public exploit code.

Affected product: Mattermost. 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-2026-3524/ (Markdown: https://insights.sbomify.com/CVE-2026-3524/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-3524
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-3524
- OSV: https://osv.dev/vulnerability/CVE-2026-3524

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-3524/
Summaries are generated and may contain mistakes; the official description above is the record.