CVE-2026-16046: Mattermost Server

Medium severity, CVSS 4.3. EPSS: 0.3% chance of exploitation in the next 30 days.

Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21 fail to enforce run-state validation on write operations for finished playbook runs which allows a run participant to modify status, checklists, retrospective content, ownership, and participants on completed runs via REST and GraphQL API requests. Mattermost Advisory ID: MMSA-2026-00675

Affected products

• Mattermost Mattermost Server: from 10.11.0, before 10.11.22 (fixed in 10.11.22); from 11.7.0, before 11.7.7 (fixed in 11.7.7)

Published 2026-08-17. Last modified 2026-08-18.