Description
Mattermost versions 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12, 11.0.x <= 11.0.3 fail to properly validate OAuth state tokens during OpenID Connect authentication which allows an authenticated attacker with team creation privileges to take over a user account via manipulation of authentication data during the OAuth completion flow. This requires email verification to be disabled (default: disabled), OAuth/OpenID Connect to be enabled, and the attacker to control two users in the SSO system with one of them never having logged into Mattermost.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Mattermost | Mattermost | 10.12.0 – ≤ 10.12.1, 10.11.0 – ≤ 10.11.4, 10.5.0 – ≤ 10.5.12, 11.0.0 – ≤ 11.0.3 | 11.1.0 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Leap 16.0 | govulncheck-vulndb | 0.0.20260723T184607-160000.1.1 | openSUSE-SU-2026:21483-1 |
| openSUSE Leap 15.6 | govulncheck-vulndb | 0.0.20251230T014957-150000.1.134.1 | SUSE-SU-2026:0037-1 |
Affected packages
| Ecosystem | Package | Affected | Fixed | Record |
|---|---|---|---|---|
| Go | github.com/mattermost/mattermost-server | >= 10.12.0, < 10.12.2 | 10.12.2 | GHSA-3x39-62h4-f8j6 |
| Go | github.com/mattermost/mattermost-server | >= 10.11.0, < 10.11.5 | 10.11.5 | GHSA-3x39-62h4-f8j6 |
| Go | github.com/mattermost/mattermost-server | >= 10.5.0, < 10.5.13 | 10.5.13 | GHSA-3x39-62h4-f8j6 |
| Go | github.com/mattermost/mattermost-server | >= 11.0.0, < 11.0.4 | 11.0.4 | GHSA-3x39-62h4-f8j6 |
| Go | github.com/mattermost/mattermost-server | all versions | — | GO-2025-4168 |
| Go | github.com/mattermost/mattermost-server/v5 | all versions | — | GO-2025-4168 |
| Go | github.com/mattermost/mattermost-server/v6 | all versions | — | GO-2025-4168 |
| Go | github.com/mattermost/mattermost/server/v8 | < 8.0.0-20251028000919-d3ed703dc833 | 8.0.0-20251028000919-d3ed703dc833 | GHSA-3x39-62h4-f8j6 |
Advisories 4
- openSUSE-SU-2026:21483-1 Security update for govulncheck-vulndb SUSE / openSUSE Security Updates · Jul 31, 2026
- SUSE-SU-2026:0037-1 Security update for govulncheck-vulndb SUSE / openSUSE Security Updates · Mar 23, 2026
- NCSC-2025-0378 Kwetsbaarheden verholpen in Mattermost NCSC-NL (Netherlands) · Nov 28, 2025
- WID-SEC-2025-2434 Mattermost Server: Mehrere Schwachstellen ermöglichen die Umgehung von Sicherheitsmaßnahmen BSI CERT-Bund (WID) · Nov 27, 2025