CVE-2026-40878 mailcow-dockerized Login Page has Reflected Parameter Injection / Wrong-Context XSS Escaping
Attackers can execute arbitrary JavaScript in the mailcow login page via reflected parameter injection, potentially leading to session hijacking or account takeover.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-40878?
CVE-2026-40878 is a low-severity cross-site scripting vulnerability in mailcow-dockerized, published on 21 Apr 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
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.
Weakness: CWE-79
Which versions are affected by CVE-2026-40878?
How do I fix CVE-2026-40878?
No fix has been published for CVE-2026-40878 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-40878 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40878 exists.
Public exploit code: 1 Nuclei template.
Sources
Also known as GHSA-xv9r-j862-5hqf.