Executive brief
Mattermost failed to enforce permission checks when creating teams with invite-controlled settings (open invite or domain restrictions). An authenticated user with team creation rights but without invite management permissions could bypass access controls by setting these options during team creation, actions they would normally be blocked from performing on existing teams. This allows unauthorized configuration of who can join a team.
Technical details
This is a missing authorization vulnerability (CWE-862) in Mattermost's team creation endpoint. The root cause is an inconsistent permission check: the PermissionInviteUser authorization was only enforced on team update/patch operations but not during initial team creation via POST /api/v4/teams. An authenticated attacker holding PermissionCreateTeam can supply allow_open_invite: true or a non-empty allowed_domains parameter to make the newly created team publicly joinable or restrict membership by domain, despite lacking PermissionInviteUser. The vulnerability requires network access to the Mattermost API and valid authentication credentials (PR:L), with no user interaction needed. The fix aligns permission checks between team creation and team update operations, enforced in patched versions 10.11.17, 11.5.5, 11.6.2, and 11.7.0.
Affected products
- Mattermost Mattermost Server 10.11.0–10.11.15, 11.5.0–11.5.4, 11.6.0–11.6.1
Timeline
- 2026-06-12: disclosed: Vulnerability published in GitHub Advisory Database and NVD
- 2026-05-04: patched: Fixes merged into release branches; patched versions released (10.11.17, 11.5.5, 11.6.2, 11.7.0)