CVE-2025-20051 - Arbitrary File Read Vulnerability in Mattermost Boards Due to Insufficient Input Validation

Mattermost, a popular open-source messaging and collaboration platform, has been found to be vulnerable to a security issue in their Boards feature, allowing an attacker to read any arbitrary file on the system. Versions 10.4.x <= 10.4.1, 9.11.x <= 9.11.7, 10.3.x <= 10.3.2, and 10.2.x <= 10.2.2 of Mattermost are affected by this vulnerability.

The issue has been assigned the CVE identifier CVE-2025-20051. In this post, we are going to discuss the details of this vulnerability, including the technical background, how the exploit works, and what you can do to mitigate the risks.

Technical Background

Mattermost Boards is part of the Mattermost suite that allows users to create, edit, and collaborate on projects using customizable boards. When duplicating or patching a board, Mattermost fails to properly validate the input provided by the user, resulting in the possibility of reading arbitrary files on the server.

Here's an example of how the exploit works

1. A user creates a board and adds a specially crafted block/link to it. This block contains a reference to a local file on the server, using a file path such as /etc/passwd.

The user duplicates this board and shares it with the attacker.

3. The attacker opens the duplicated board and, due to insufficient input validation, is able to read the contents of the arbitrary file /etc/passwd that the crafted block is pointing to.

This code snippet demonstrates the input in the block

{
    "type": "file_reference",
    "file_path": "../../../../../../etc/passwd"
}

The exploitation details show that this vulnerability can allow anyone with the ability to create or edit boards to potentially access sensitive data on the server by crafting malicious blocks that point to arbitrary files.

This vulnerability was reported and discussed in the following sources

- Mattermost's Security Advisory: link
- Mattermost's Release Notes: link

Mitigation

To address this vulnerability, Mattermost has released security updates in its latest versions. Users are highly encouraged to update their Mattermost installations to one of the following versions:

10.2.3 or later for 10.2.x series

Additionally, it is advisable to restrict access to board editing and duplication functionalities only to trusted users, to minimize the risk of a potential attack.

Conclusion

The arbitrary file read vulnerability in Mattermost Boards (CVE-2025-20051) is a dangerous security flaw that can allow an attacker to gain access to sensitive data on the server. By updating to the latest version of Mattermost and practicing proper access control management, users of the platform can protect their systems and mitigate the risks associated with this vulnerability.

Timeline

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