medium4.3
CVE-2026-21386
Mattermost fails to use consistent error responses when handling the /mute command
Impact
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 packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| go | github.com/mattermost/mattermost/server/v8 | < 8.0.0-20260130144323-5bb5261c72fa | 8.0.0-20260130144323-5bb5261c72fa |
| go | github.com/mattermost/mattermost-server | < 5.3.2-0.20260130144323-5bb5261c72fa | 5.3.2-0.20260130144323-5bb5261c72fa |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Mattermost | Mattermost Server | from 10.11.0 before 10.11.11 from 11.2.0 before 11.2.3 from 11.3.0 before 11.3.1 |