CVE-2026-40878: Mailcow Mailcow-Dockerized

Low severity, CVSS 2.1. EPSS: 1% 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 mailcow web interface passes the raw `$_SERVER['REQUEST_URI']` to Twig as a global template variable and renders it inside a JavaScript string literal in the `setLang()` helper of `base.twig`, relying on Twig's default HTML auto-escaping instead of the context-appropriate `js` escaping strategy. In addition, the `query_string()` Twig helper merges all current `$_GET` parameters into the language-switching links on the login page, so attacker-supplied parameters are reflected and preserved across navigation. 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.