Path traversal in Vanquish Upload Files for WooCommerce

The Vanquish Upload Files for WooCommerce plugin for WordPress is vulnerable to Directory Traversal in all versions up to, and including, 2.7.13 via the 'vanupfi_file_name' parameter parameter. This makes it possible for authenticated attackers, with subscriber-level access and above, to read the contents of arbitrary files on the server, which can contain sensitive information. The authorization bypass is achieved by supplying a non-existent order ID (e.g., '.pdf'), which causes wc_get_order() to return false and short-circuits the vanupfi_user_can_access_order_files() check, while the is_pdf() branch selector's loose strpos() substring match allows a traversal payload such as '../.pdf/../../../../wp-config.php' to satisfy the PDF branch and be streamed verbatim via readfile().