Description
Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to sanitize the active channel field returned by the user status API endpoints, which allows an authenticated user to learn the channel ID of a private channel another user is actively viewing via the status endpoints, without being a member of that channel. Mattermost Advisory ID: MMSA-2026-00765
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Mattermost | Mattermost | 11.9.0 – ≤ 11.9.1, 11.8.0 – ≤ 11.8.5, 11.7.0 – ≤ 11.7.10, 11.10.0 – ≤ 11.10.1 | 11.11.0 |
Advisories 1
- WID-SEC-2026-4009 Mattermost: Mehrere Schwachstellen BSI CERT-Bund (WID) · Oct 15, 2026
References
- MMSA-2026-00765 vendor-advisory