GHSA-mpc7-mm28-f6wq Mattermost allows authenticated guest users to enumerate user IDs outside their allowed visibility scope

• Go github.com/mattermost/mattermost/server/v8: >= 11.4.0, < 11.4.1 → fixed in 11.4.1 • Go github.com/mattermost/mattermost/server/v8: >= 11.3.0-rc1, < 11.3.2 → fixed in 11.3.2 • Go github.com/mattermost/mattermost/server/v8: >= 11.2.0-rc1, < 11.2.3 → fixed in 11.2.3 • Go github.com/mattermost/mattermost/server/v8: >= 10.11.0-rc1, < 10.11.11 → fixed in 10.11.11 • Go github.com/mattermost/mattermost/server/v8: >= 8.0.0-20260105080200-d27a2195068d, < 8.0.0-20260217110922-b7d4a1f1f59b → fixed in 8.0.0-20260217110922-b7d4a1f1f59b

Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to apply view restrictions when retrieving group member IDs, which allows authenticated guest users to enumerate user IDs outside their allowed visibility scope via the group retrieval endpoint. Mattermost Advisory ID: MMSA-2026-00594.