Improper file ownership validation in the Boards API allows unauthorised file access
Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate file ownership and access control, which allows an authenticated user to access and download files belonging to other users or teams via crafted Boards API requests using valid file IDs.. Mattermost Advisory ID: MMSA-2026-00620
Problem Types
| Type | CWE ID | Description |
|---|
| CWE | CWE-639 | CWE-639: Authorization Bypass Through User-Controlled Key |
Type: CWE
Description: CWE-639: Authorization Bypass Through User-Controlled Key
Metrics
| Version | Base score | Base severity | Vector |
|---|
| 3.1 | 5.9 | MEDIUM | CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N |
Version: 3.1
Base score: 5.9
Base severity: MEDIUM
Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N