Mattermost versions 10.5.x <= 10.5.8, 9.11.x <= 9.11.17 fail to properly validate authorization for team scheme role modifications which allows Team Admins to demote Team Members to Guests via the PUT /api/v4/teams/team-id/members/user-id/schemeRoles API endpoint.
| Package (Ecosystem) | Introduced | Fixed | Limit |
|---|---|---|---|
| github.com/mattermost/mattermost-server(Go) | 10.5.0 | 10.5.9 | N/A |
| github.com/mattermost/mattermost-server(Go) | 9.11.0 | 9.11.18 | N/A |
| github.com/mattermost/mattermost/server/v8(Go) | 0 | 8.0.0-20250721095846-c602a4a78e1f | N/A |
| github.com/mattermost/mattermost-server/v5(Go) | 0 | N/A | N/A |
| github.com/mattermost/mattermost-server/v6(Go) | 0 | N/A | N/A |
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