CVE-2026-9820: Mattermost Server

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

Mattermost versions 11.7.x <= 11.7.2, 10.11.x <= 10.11.19 fail to sanitize team objects returned by the scheme teams endpoint, which allows a user with the User Manager role to obtain invite links for private teams and use them to join or share access to those teams via the scheme teams API endpoint.. Mattermost Advisory ID: MMSA-2026-00671

Affected products

• Mattermost Mattermost Server: from 10.11.0, before 10.11.20 (fixed in 10.11.20); from 11.7.0, before 11.7.3 (fixed in 11.7.3)

Published 2026-07-13. Last modified 2026-07-13.