| Package | Affected versions | Patched versions |
|---|---|---|
| github.com/mattermost/mattermost-server | ≥ 10.11.0-rc1, < 10.11.12≥ 10.11.0-rc1+incompatible, < 10.11.12+incompatible≥ 11.2.0-rc1, < 11.2.4≥ 11.2.0-rc1+incompatible, < 11.2.4+incompatible≥ 11.3.0-rc1, < 11.3.2≥ 11.3.0-rc1+incompatible, < 11.3.2+incompatible≥ 11.4.0-rc1, < 11.4.1≥ 11.4.0-rc1+incompatible, < 11.4.1+incompatible | 10.11.1210.11.12+incompatible11.2.411.2.4+incompatible11.3.211.3.2+incompatible11.4.111.4.1+incompatible |
| github.com/mattermost/mattermost-server/v5 | all versions | |
| github.com/mattermost/mattermost-server/v6 | all versions | |
| github.com/mattermost/mattermost/server/v8 | ≥ 8.0.0-20260105080200-d27a2195068d, < 8.0.0-20260217110922-b7d4a1f1f59b | 8.0.0-20260217110922-b7d4a1f1f59b |
| mattermost server | ≥ 10.11.0, < 10.11.12≥ 11.2.0, < 11.2.4≥ 11.3.0, < 11.3.2≥ 11.4.0, < 11.4.1 | 10.11.1211.2.411.3.211.4.1 |
Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to properly validate user identity in the OpenID {{IsSameUser()}} comparison logic, which allows an attacker to take over arbitrary user accounts via an overly permissive substring matching flaw in the user discovery flow. Mattermost Advisory ID: MMSA-2026-00590
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