MEDIUM 4.3 Go
Mattermost allows authenticated guest users to enumerate user IDs outside their allowed visibility scope
GHSA-mpc7-mm28-f6wq · CVE-2026-3115 · GO-2026-5512
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Description
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.
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