CVE-2025-25279: Mattermost Vulnerability in Board Import Validation Allows Arbitrary File Reading

In this post, we will discuss a recent security vulnerability identified in various versions of Mattermost, an open-source messaging and collaboration platform. This vulnerability, tracked as CVE-2025-25279, affects Mattermost 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. To put it simply, this vulnerability could potentially allow an attacker to read any arbitrary file on the system by importing and exporting a malicious import archive in Boards. In this post, we will walk through the exploit details, provide a code snippet illustrating the issue, and share links to the original references for this vulnerability.

Exploit Details

The vulnerability CVE-2025-25279 stems from a validation issue in Mattermost versions as listed above, where the application does not adequately validate board blocks when importing boards. Consequently, an attacker can exploit this flaw to read any arbitrary file on the system. For this attack to be successful, the attacker needs to create a specially crafted import archive and import it to the affected Mattermost instance. The attacker then exports the same archive, enabling them to gain access to sensitive system information that should otherwise not be accessible.

Imagine the following piece of code in Mattermost's board import validation process

def import_board(archive):
    # Unpack the archive file
    board_data = unpack_archive(archive)

    # Validate the board_data
    if not validate_board(board_data):
        raise ValueError("Invalid board data")

    # Import the board to the system
    saved_board = save_board(board_data)

    return saved_board

Save the board_data to the system

However, due to insufficient validation, an attacker could manipulate the board_data to include malicious information, such as a reference to an arbitrary file on the system.

Suppose the attacker creates an archive file that contains the following malicious board_data

{"file_path": "../../../../../../etc/passwd"}

Since the validation process is not robust enough, the attacker can successfully import the malicious data into the system and subsequently export it, revealing sensitive system information.

For more information on this vulnerability, please refer to the following resources

- Mattermost Security Updates
- CVE-2025-25279 Description by NVD
- GitHub Security Advisory

Conclusion

CVE-2025-25279 is an important security vulnerability that can be exploited to gain unauthorized access to sensitive information on the system. If you are running an affected version of Mattermost, it is highly recommended that you apply the appropriate security updates or patches to protect your system from potential attacks. Furthermore, always be vigilant about the origin of imported data in any application, ensuring that proper validation and sanitization processes are in place to minimize the risks associated with such vulnerabilities.

Timeline

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