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 limit the length of the post ID array accepted by the bulk reactions endpoint which allows an authenticated user to cause excessive database load via a crafted request to {{POST /api/v4/posts/ids/reactions}}.. Mattermost Advisory ID: MMSA-2026-00771
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-2026-3519 Mattermost Server: Mehrere Schwachstellen BSI CERT-Bund (WID) · Sep 22, 2026
References
- MMSA-2026-00771 vendor-advisory