---
id: CVE-2026-5163
title: >-
  Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when
  processing AI-assisted message rewrites which allows an authenticated attacker
  to read the content of threads in private channels and direct messages they do
  not…
summary: >-
  Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when
  processing AI-assisted message rewrites which allows an authenticated attacker
  to read the content of threads in private channels and direct messages they do
  not…
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N'
cwe:
  - CWE-862
vendor: mattermost
product: mattermost_server
affected:
  - 'mattermost_server >= 11.5.0, < 11.5.2'
patched:
  - mattermost_server 11.5.2
published: '2026-05-18'
updated: '2026-10-14'
sourceUpdated: '2026-10-14T20:10:00.190'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-5163'
references:
  - url: 'https://mattermost.com/security-updates'
    label: responsibledisclosure@mattermost.com
tags:
  - nvd
epss: 0.0034
epssPercentile: 0.25816
ingestedAt: '2026-10-14T20:53:12.299Z'
---

## Overview

Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite endpoint.. Mattermost Advisory ID: MMSA-2026-00645

## Affected

- `mattermost_server >= 11.5.0, < 11.5.2`

## Remediation

Upgrade past the affected range:

- `mattermost_server 11.5.2`