CVE-2026-40875: Mailcow Mailcow-Dockerized

High severity, CVSS 7.0. EPSS: 0.3% 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 user dashboard's "Seen successful connections" (login history) renders the client IP from login logs without HTML escaping. Because the server trusts the X-Real-IP header as the source IP for logging, an attacker can inject HTML/JS into this field. This Self-XSS can be exploited by a Login CSRF to force the victim into the attacker's account, and then read emails in a previous browser tab. 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.