GHSA-8r89-8w26-cq32MediumCVSS 6.5

Mattermost doesn't verify channel membership when processing AI-assisted message rewrites

Published
May 18, 2026
Last Modified
June 1, 2026

🔗 CVE IDs covered (1)

CVE-2026-5163 →

📋 Description

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 products3

  • go/github.com/mattermost/mattermost/server/v8:>= 11.5.0, < 11.5.2
  • go/github.com/mattermost/mattermost/server/v8:< 8.0.0-20260401090745-f4d1abe7e8f5
  • go/github.com/mattermost/mattermost-server:< 5.3.2-0.20260401090745-f4d1abe7e8f5

🔗 References (4)