rConfig 3.9.4 and earlier allows authenticated code execution (of system commands) by sending a forged GET request to lib/ajaxHandlers/ajaxAddTemplate.php or lib/ajaxHandlers/ajaxEditTemplate.php.

rConfig 3.9.4 is vulnerable to remote code execution due to improper validation in the file upload functionality. vendor.crud.php accepts a file upload by checking content-type without considering the file extension and header. Thus, an attacker can exploit this by uploading a .php file to vendor.php that contains arbitrary PHP code and changing the content-type to image/gif.

rConfig 3.9.4 is vulnerable to cross-site request forgery (CSRF) because it lacks implementation of CSRF protection such as a CSRF token. An attacker can leverage this vulnerability by creating a form (add a user, delete a user, or edit a user).

rConfig 3.9.4 is vulnerable to session fixation because session expiry and randomization are mishandled. The application can reuse a session via PHPSESSID. Also, an attacker can exploit this vulnerability in conjunction with CVE-2020-12256 or CVE-2020-12259.