Overview
The vulnerability in focus, CVE-2025-4981, presents a significant security threat to a host of Mattermost versions. As a widely used open-source, self-hosted online chat service, Mattermost has a broad range of commercial and non-commercial users globally. The vulnerability arises from the failure of these versions to sanitize filenames in the archive extractor, thereby providing authenticated users the potential to write files anywhere on the filesystem. This vulnerability can lead to remote code execution and consequently, a considerable system compromise or data leakage.
Given the severity of the potential impact, understanding this vulnerability is of paramount importance to cybersecurity professionals, system administrators, and anyone who relies on Mattermost for their communication needs. It calls for immediate attention and mitigation to safeguard the integrity of these systems.
Vulnerability Summary
CVE ID: CVE-2025-4981
Severity: Critical (CVSS score 9.9)
Attack Vector: Network
Privileges Required: User
User Interaction: Required
Impact: System compromise, potential data leakage
Affected Products
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Product | Affected Versions
Mattermost | 10.5.x <= 10.5.5 Mattermost | 9.11.x <= 9.11.15 Mattermost | 10.8.x <= 10.8.0 Mattermost | 10.7.x <= 10.7.2 Mattermost | 10.6.x <= 10.6.5 How the Exploit Works
The exploit leverages the vulnerability in Mattermost’s archive extraction process. An authenticated user can upload an archive with a malicious filename containing path traversal sequences. Mattermost’s failure to sanitize these filenames allows the file to be written to any location on the filesystem. This capability can lead to remote code execution if a malicious user manages to place an executable file in a directory where it can be run automatically or by a privileged user.
Conceptual Example Code
Here’s a conceptual example of how an exploit using a malicious archive might work:
POST /api/v4/files HTTP/1.1
Host: mattermost.example.com
Authorization: Bearer <access-token>
Content-Type: multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW
------WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="files"; filename="../../../etc/cron.d/malicious"
Content-Type: application/gzip
{ binary data }
------WebKitFormBoundary7MA4YWxkTrZu0gW--In this example, an HTTP POST request is made to the Mattermost file upload API endpoint. The archive contains a file with a path traversal sequence in the filename (`../../../etc/cron.d/malicious`). This file could contain instructions for a cron job that executes a malicious script, potentially leading to remote code execution.