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.