Admidio is a free, open source user management system for websites of organizations and groups. In Admidio before version 4.3.10, there is a Remote Code Execution Vulnerability in the Message module of the Admidio Application, where it is possible to upload a PHP file in the attachment. The uploaded file can be accessed publicly through the URL `{admidio_base_url}/adm_my_files/messages_attachments/{file_name}`. The vulnerability is caused due to the lack of file extension verification, allowing