---
id: CVE-2026-19603
title: >-
  Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10,
  11.10.x <= 11.10.1 fail to sanitize the active channel field returned by the
  user status API endpoints, which allows an authenticated user to learn the
  channel ID…
summary: >-
  Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10,
  11.10.x <= 11.10.1 fail to sanitize the active channel field returned by the
  user status API endpoints, which allows an authenticated user to learn the
  channel ID…
severity: medium
cvss: 4.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N'
cwe:
  - CWE-201
vendor: Mattermost
product: Mattermost
affected:
  - Mattermost >= 11.9.0 <= 11.9.1
  - Mattermost >= 11.8.0 <= 11.8.5
  - Mattermost >= 11.7.0 <= 11.7.10
  - Mattermost >= 11.10.0 <= 11.10.1
published: '2026-10-16'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T19:23:18.623'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-19603'
references:
  - url: 'https://mattermost.com/security-updates'
    label: responsibledisclosure@mattermost.com
tags:
  - nvd
  - cve.org
epss: 0.00176
epssPercentile: 0.071
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-10-16T11:58:53.325388Z'
ingestedAt: '2026-10-16T08:02:23.122Z'
---

## Overview

Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to sanitize the active channel field returned by the user status API endpoints, which allows an authenticated user to learn the channel ID of a private channel another user is actively viewing via the status endpoints, without being a member of that channel. Mattermost Advisory ID: MMSA-2026-00765

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.