CVE-2026-8823: Mattermost Server

Low severity, CVSS 3.8. EPSS: 0.3% chance of exploitation in the next 30 days.

Mattermost versions 11.7.x <= 11.7.0, 10.11.x <= 10.11.17 fail to validate bot targets when demoting users to guests which allows a lower-privileged administrator to degrade arbitrary bot accounts via the standard demote-user API.. Mattermost Advisory ID: MMSA-2026-00669

Affected products

• Mattermost Mattermost Server: from 10.11.0, before 10.11.18 (fixed in 10.11.18); from 11.7.0, before 11.7.1 (fixed in 11.7.1)

Published 2026-06-22. Last modified 2026-06-26.