HAX CMS PHP allows users to manage their microsite universe with a PHP backend. Prior to version 11.0.3, the `gitImportSite` functionality obtains a URL string from a POST request and insufficiently validates user input. The `set_remote` function later passes this input into `proc_open`, yielding OS command injection. An authenticated attacker can craft a URL string that bypasses the validation checks employed by the `filter_var` and `strpos` functions in order to execute arbitrary OS commands on the backend server. The attacker can exfiltrate command output via an HTTP request. Version 11.0.3 contains a patch for the issue.