Checkout Custom Fields Builder for WooCommerce <= 1.1.5 - Missing Authorization to Authenticated (Subscriber+) Arbitrary Plugin Installation via 'plugin' Parameter

The Checkout Custom Fields Builder for WooCommerce plugin for WordPress is vulnerable to authorization bypass in all versions up to, and including, 1.1.5. This is due to the plugin not properly verifying that a user is authorized to perform an action. This makes it possible for authenticated attackers, with subscriber-level access and above, to install and activate an arbitrary attacker-hosted plugin, resulting in remote code execution on the server. The required nonce is emitted inline on all admin pages accessible to subscribers when WooCommerce is inactive, meaning any subscriber-level user can harvest it and trigger the exploit without any additional privileges.