Printcart Web to Print Product Designer for WooCommerce <= 2.8.5 - Unauthenticated Arbitrary File Read via 'folder' and 'mockups' Parameters

The Printcart Web to Print Product Designer for WooCommerce plugin for WordPress is vulnerable to Directory Traversal in all versions up to, and including, 2.8.5 via the 'mockups' parameter. This makes it possible for unauthenticated attackers to read the contents of arbitrary files on the server, which can contain sensitive information. A valid nonce is obtainable by unauthenticated users via the companion nbd_check_use_logged_in nopriv AJAX endpoint, which freely mints and returns a nbdesigner-get-data nonce to any visitor; additionally, if the NBDESIGNER_ENABLE_NONCE constant is disabled, even this nonce gate is bypassed entirely.