CVE-2026-5163 — Mattermost versions 11.5.x <= 11.5.1 fail to verify channel

title: CVE-2026-5163 - Mattermost Unauthenticated Channel Access via Rewrite Endpoint
id: scw-2026-05-18-ai-1
status: experimental
level: critical
description: |
  Detects attempts to access private channels or direct messages in Mattermost by exploiting CVE-2026-5163. This rule specifically targets the '/api/v4/posts/rewrite' endpoint which is used in the vulnerability to bypass channel membership verification. An authenticated attacker could use this to read sensitive information.
author: SCW Feed Engine (AI-generated)
date: 2026-05-18
references:
  - https://shimiscyberworld.com/posts/nvd-CVE-2026-5163/
tags:
  - attack.privilege_escalation
  - attack.t1078.004
logsource:
    category: webserver
detection:
  selection:
      cs-uri|contains:
          - '/api/v4/posts/rewrite'
      cs-method:
          - 'POST'
      condition: selection
falsepositives:
  - Legitimate administrative activity

Source: Shimi's Cyber World · License & reuse