CVE-2026-3472: Mattermost Server

Low severity, CVSS 3.5. EPSS: 0.3% chance of exploitation in the next 30 days.

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

• Mattermost Mattermost Server: from 10.11.0, before 10.11.19 (fixed in 10.11.19); from 11.5.0, before 11.5.7 (fixed in 11.5.7); from 11.6.0, before 11.6.4 (fixed in 11.6.4)

Published 2026-06-26. Last modified 2026-06-29.