CVE-2026-40873: Mailcow Mailcow-Dockerized

High severity, CVSS 8.9. EPSS: 0.6% chance of exploitation in the next 30 days.

mailcow: dockerized is an open source groupware/email suite based on docker. In versions prior to 2026-03b, the Quarantine details modal injects attachment filenames into HTML without escaping, allowing arbitrary HTML/JS execution. An attacker can deliver an email with a crafted attachment name so that when an admin views the quarantine item, JavaScript executes in their browser, taking over their account. Version 2026-03b fixes the vulnerability.

Affected products

• Mailcow Mailcow-Dockerized: before 2026-03b (fixed in 2026-03b)

Published 2026-04-21. Last modified 2026-06-17.