Missing authorization in Funnelkit Automations

The FunnelKit Automations – Email Marketing Automation and CRM for WordPress & WooCommerce plugin for WordPress is vulnerable to Missing Authorization in all versions up to, and including, 3.6.4.1. This is due to the plugin not properly verifying that a user is authorized to perform administrative actions in the `bwfan_test_email` AJAX handler. The nonce used for verification is publicly exposed to all visitors (including unauthenticated users) via the frontend JavaScript localization, and the `check_nonce()` function accepts low-privilege authenticated users who possess this nonce. This makes it possible for authenticated attackers, with Subscriber-level access and above, to send arbitrary emails from the site with attacker-controlled subject and body content.