Description
Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to use consistent error responses when handling the /mute command which allows an authenticated team member to enumerate private channels they are not authorized to know about via differing error messages for nonexistent versus private channels. Mattermost Advisory ID: MMSA-2026-00588
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Mattermost | Mattermost | 11.3.0 – ≤ 11.3.0, 11.2.0 – ≤ 11.2.2, 10.11.0 – ≤ 10.11.10 | 11.4.0 |
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 | 0.0.20260326T203309-150000.1.155.2 | SUSE-SU-2026:1135-1 |
Affected packages
| Ecosystem | Package | Affected | Fixed | Record |
|---|---|---|---|---|
| Go | github.com/mattermost/mattermost-server | < 5.3.2-0.20260130144323-5bb5261c72fa | 5.3.2-0.20260130144323-5bb5261c72fa | GHSA-5mr9-crcg-8wh2 |
| Go | github.com/mattermost/mattermost-server | >= 10.11.0-rc1, < 10.11.11 | 10.11.11 | GHSA-5mr9-crcg-8wh2 |
| Go | github.com/mattermost/mattermost-server | >= 11.2.0-rc1, < 11.2.3 | 11.2.3 | GHSA-5mr9-crcg-8wh2 |
| Go | github.com/mattermost/mattermost-server | >= 11.3.0-rc1, < 11.3.1 | 11.3.1 | GHSA-5mr9-crcg-8wh2 |
| Go | github.com/mattermost/mattermost-server | >= 10.11.0-rc1+incompatible, < 10.11.11+incompatible · >= 11.2.0-rc1+incompatible, < 11.2.3+incompatible · >= 11.3.0-rc1+incompatible, < 11.3.1+incompatible | 10.11.11+incompatible, 11.2.3+incompatible, 11.3.1+incompatible | GO-2026-4744 |
| Go | github.com/mattermost/mattermost-server/v5 | all versions | — | GO-2026-4744 |
| Go | github.com/mattermost/mattermost-server/v6 | all versions | — | GO-2026-4744 |
| Go | github.com/mattermost/mattermost/server/v8 | < 8.0.0-20260130144323-5bb5261c72fa | 8.0.0-20260130144323-5bb5261c72fa | GHSA-5mr9-crcg-8wh2 |
Advisories 3
- openSUSE-SU-2026:21483-1 Security update for govulncheck-vulndb SUSE / openSUSE Security Updates · Jul 31, 2026
- SUSE-SU-2026:1135-1 Security update for govulncheck-vulndb SUSE / openSUSE Security Updates · Mar 31, 2026
- WID-SEC-2026-0422 Mattermost: Mehrere Schwachstellen BSI CERT-Bund (WID) · Mar 19, 2026
References
- MMSA-2026-00588 vendor-advisory