Description
Mattermost versions 10.11.x <= 10.11.18, 11.6.x <= 11.6.3, 11.5.x <= 11.5.6 fail to properly apply markdown image rendering restrictions to AI bot tool result posts, which allows an authenticated attacker to exfiltrate data to an attacker-controlled server via injecting markdown image syntax into tool result content rendered by a victim's client.. Mattermost Advisory ID: MMSA-2026-00619
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Mattermost | Mattermost | 10.11.0 – ≤ 10.11.18, 11.6.0 – ≤ 11.6.3, 11.5.0 – ≤ 11.5.6 | 11.7.0 |
Advisories 1
- WID-SEC-2026-1705 Mattermost Server und Plugins: Mehrere Schwachstellen ermöglichen nicht spezifizierten Angriff BSI CERT-Bund (WID) · Jun 28, 2026
References
- MMSA-2026-00619 vendor-advisory