CVE-2026-40878 PoC — mailcow-dockerized Login Page has Reflected Parameter Injection / Wrong-Context XSS Escaping

Source

https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-40878.yaml

Associated Vulnerability

Title:mailcow-dockerized Login Page has Reflected Parameter Injection / Wrong-Context XSS Escaping (CVE-2026-40878)
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.

Description

mailcow < 2026-03b reflects raw REQUEST_URI into JavaScript and href links on the login page, allowing attackers to inject parameters that break JS logic and enable phishing.

File Snapshot

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