---
id: CVE-2025-12689
title: >-
  Mattermost versions 11.0.x <= 11.0.4, 10.12.x <= 10.12.2, 10.11.x <= 10.11.6
  fail to check WebSocket request field for proper UTF-8 format, which allows
  attacker to crash Calls plug-in via sending malformed request.
summary: >-
  Mattermost versions 11.0.x <= 11.0.4, 10.12.x <= 10.12.2, 10.11.x <= 10.11.6
  fail to check WebSocket request field for proper UTF-8 format, which allows
  attacker to crash Calls plug-in via sending malformed request.
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-1287
vendor: mattermost
product: mattermost_server
affected:
  - 'mattermost_server >= 10.11.0, < 10.11.7'
  - 'mattermost_server >= 10.12.0, < 10.12.3'
  - 'mattermost_server >= 11.0.0, < 11.0.5'
patched:
  - mattermost_server 11.0.5
published: '2025-12-17'
updated: '2026-10-13'
sourceUpdated: '2026-10-13T11:10:00.203'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-12689'
references:
  - url: 'https://mattermost.com/security-updates'
    label: responsibledisclosure@mattermost.com
tags:
  - nvd
epss: 0.00288
epssPercentile: 0.19656
ingestedAt: '2026-10-13T11:23:51.121Z'
---

## Overview

Mattermost versions 11.0.x <= 11.0.4, 10.12.x <= 10.12.2, 10.11.x <= 10.11.6 fail to check WebSocket request field for proper UTF-8 format, which allows attacker to crash Calls plug-in via sending malformed request.

## Affected

- `mattermost_server >= 10.11.0, < 10.11.7`
- `mattermost_server >= 10.12.0, < 10.12.3`
- `mattermost_server >= 11.0.0, < 11.0.5`

## Remediation

Upgrade past the affected range:

- `mattermost_server 11.0.5`