Email Customizer for WooCommerce (Pro) <= 3.9.5 - Authenticated (Subscriber+) Remote Code Execution via 'template' Parameter

The Email Customizer for WooCommerce (Pro) plugin for WordPress is vulnerable to Remote Code Execution in versions up to, and including, 3.9.5. This is due to insufficient authorization and input sanitization in the send_test_mail() function, which allows user-controlled PHP code to be written to executable files in the uploads directory. This makes it possible for authenticated attackers, with subscriber-level access and above, to execute arbitrary PHP code on the server, leading to full site compromise.