Description
Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10 fail to validate the target post ID in the Agents plugin's mention reminder component, which allows an authenticated user who can post in a channel visible to a system administrator to cause the administrator's browser to send an unintended API request, resulting in replacement of an installed plugin and code execution on the server, via a crafted post containing a forged mention reminder that the administrator clicks. Mattermost Advisory ID: MMSA-2026-00742
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 |
Advisories 1
- WID-SEC-2026-4258 Mattermost: Schwachstelle ermöglicht Codeausführung BSI CERT-Bund (WID) · Oct 29, 2026
References
- MMSA-2026-00742 vendor-advisory