Description
Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to validate that users have read access to a channel before linking a board to it, which allows an authenticated attacker to discover the membership of private channels on the same team via creating, patching, importing, or bulk-creating boards with an arbitrary channelId. Mattermost Advisory ID: MMSA-2026-00674
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Mattermost | Mattermost | 11.7.0 – ≤ 11.7.6, 10.11.0 – ≤ 10.11.21, 11.8.0 – ≤ 11.8.3 | 11.9.0 |
Advisories 2
- NCSC-2026-0305 Kwetsbaarheden verholpen in Mattermost NCSC-NL (Netherlands) · Aug 19, 2026
- WID-SEC-2026-2411 Mattermost: Mehrere Schwachstellen ermöglichen nicht spezifizierten Angriff BSI CERT-Bund (WID) · Aug 17, 2026
References
- MMSA-2026-00674 vendor-advisory