GHSA-fg35-5rf6-qg3g
Mattermost allows attackers to take over arbitrary user accounts via overly permissive substring matching flaw
Packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| Go | github.com/mattermost/mattermost-server | >= 11.4.0-rc1, < 11.4.1 | 11.4.1 |
| Go | github.com/mattermost/mattermost-server | >= 11.3.0-rc1, < 11.3.2 | 11.3.2 |
| Go | github.com/mattermost/mattermost-server | >= 11.2.0-rc1, < 11.2.4 | 11.2.4 |
| Go | github.com/mattermost/mattermost-server | >= 10.11.0-rc1, < 10.11.12 | 10.11.12 |
| Go | github.com/mattermost/mattermost/server/v8 | >= 8.0.0-20260105080200-d27a2195068d, < 8.0.0-20260217110922-b7d4a1f1f59b | 8.0.0-20260217110922-b7d4a1f1f59b |
Details
As written in the advisory (Markdown source, shown as plain text).
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
References
External links from the advisory. They lead to third-party sites.