Ninja Forms - File Uploads <= 3.3.29 - Unauthenticated Arbitrary File Read via File Upload Field 'files[].data.file_path' Parameter

The Ninja Forms - File Uploads plugin for WordPress is vulnerable to Arbitrary File Read via the attach_files() function in versions up to, and including, 3.3.29. This is due to the get_files_for_attachment() function accepting a raw attacker-controlled 'files' array when the process() method returns early due to a client-supplied saveProgress flag, bypassing all upload validation, path normalization, and database record creation steps, and allowing an attacker-supplied file_path value to reach wp_mail() as an email attachment with only a file_exists() check. This makes it possible for unauthenticated attackers to read arbitrary files on the affected site's server.