Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fails to validate WebSocket command field types which allows an authenticated user to crash the plugin process and deny service to all Boards users via a custom_focalboard_SUBSCRIBE_TEAM message with a non-string teamId.. Mattermost Advisory ID: MMSA-2026-00687
Weakness
The product does not correctly convert an object, resource, or structure from one type to a different type.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Mattermost_server | Mattermost | 10.11.0 (including) | 10.11.22 (excluding) |
| Mattermost_server | Mattermost | 11.7.0 (including) | 11.7.7 (excluding) |
| Mattermost_server | Mattermost | 11.8.0 (including) | 11.8.4 (excluding) |