CVE-2026-3471: Mattermost Desktop

Medium severity, CVSS 6.5. EPSS: 0.3% chance of exploitation in the next 30 days.

Mattermost Desktop App versions <=6.1 6.0.1 5.4.13.0 fail to prevent an invalid URL from loading in a pop-up window in the Mattermost Desktop App which allows a malicious server owner to repeated crash the application via calling {{window.open('javascript:alert()');}}. Mattermost Advisory ID: MMSA-2026-00618

Affected products

• Mattermost Mattermost Desktop: up to and including 5.4.13.0; from 6.0.0, up to and including 6.0.1; from 6.1.0, before 6.2.0 (fixed in 6.2.0)

Published 2026-05-18. Last modified 2026-06-17.