low3.1
CVE-2026-20796
Mattermost doesn't properly validate channel membership at the time of data retrieval
Impact
Mattermost versions 10.11.x <= 10.11.9 fail to properly validate channel membership at the time of data retrieval which allows a deactivated user to learn team names they should not have access to via a race condition in the /common_teams API endpoint.. Mattermost Advisory ID: MMSA-2025-00549
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| go | github.com/mattermost/mattermost-server | >= 10.11.0, <= 10.11.9 | 10.11.10 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Mattermost | Mattermost Server | from 10.11.0 before 10.11.10 |