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.