Unauthenticated WebSocket binary frame causes denial of service in Mattermost Server
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 properly validate msgpack-encoded WebSocket frames before memory allocation which allows an unauthenticated remote attacker to crash the server process and cause a full service outage for all users via a crafted binary WebSocket message sent to the public WebSocket endpoint.. Mattermost Advisory ID: MMSA-2026-00647
Problem Types
| Type | CWE ID | Description |
|---|
| CWE | CWE-789 | CWE-789: Memory Allocation with Excessive Size Value |
Type: CWE
Description: CWE-789: Memory Allocation with Excessive Size Value
Metrics
| Version | Base score | Base severity | Vector |
|---|
| 3.1 | 7.5 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
Version: 3.1
Base score: 7.5
Base severity: HIGH
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H