# CVE-2021-37862: Business logic in Mattermost

> Attackers can trick users into signing up with attacker-controlled emails via crafted invitation tokens, potentially leading to account takeover.

- **Severity:** Low 3.7 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 17 Dec 2021
- **Updated:** 4 Aug 2024
- **Also known as:** BIT-mattermost-2021-37862, GHSA-5ffg-379q-g96f

## What is CVE-2021-37862?

CVE-2021-37862 is a low-severity vulnerability in Mattermost Mattermost Server, published on 17 Dec 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

Mattermost 6.0 and earlier fails to sufficiently validate the email address during registration, which allows attackers to trick users into signing up using attacker-controlled email addresses via crafted invitation token.

Weakness: CWE-754 (Improper Check for Unusual or Exceptional Conditions)

## Which versions are affected by CVE-2021-37862?

1 open source package ship an affected version, including mattermost. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mattermost` | Bitnami | All versions | 6.0.1 |

Products: Mattermost Mattermost Server.

## How do I fix CVE-2021-37862?

Upgrade mattermost to 6.0.1 or later.

## Is CVE-2021-37862 being exploited?

There is no known exploitation of CVE-2021-37862 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-2021-37862 and fix it if it is affected.

What it is: CVE-2021-37862 is a low-severity vulnerability in Mattermost Mattermost Server, published on 17 Dec 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-37862 in the wild and no public exploit code.

Affected packages and fixed versions:
- mattermost (Bitnami): affected all versions; fixed in 6.0.1

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-2021-37862/ (Markdown: https://insights.sbomify.com/CVE-2021-37862/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-37862
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-37862
- OSV: https://osv.dev/vulnerability/CVE-2021-37862

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-37862/
Summaries are generated and may contain mistakes; the official description above is the record.