CVE-2026-41228: Froxlor has Local File Inclusion via path traversal in API `def_language` parameter that leads to Remote Code Execution

Froxlor is open source server administration software. Prior to version 2.3.6, the Froxlor API endpoint Customers.update (and Admins.update) does not validate the deflanguage parameter against the list of available language files. An authenticated customer can set deflanguage to a path traversal payload (e.g., ../../../../../var/customers/webs/customer1/evil), which is stored in the database. On subsequent requests, Language::loadLanguage() constructs a file path using this value and executes it via require, achieving arbitrary PHP code execution as the web server user. Version 2.3.6 fixes the issue.