Notification for Telegram <= 3.3.1 - Missing Authorization to Authenticated (Subscriber+) Send Telegram Test Message

The Notification for Telegram plugin for WordPress is vulnerable to unauthorized test message sending due to a missing capability check on the 'nftb_test_action' function in versions up to, and including, 3.3.1. This makes it possible for authenticated attackers, with subscriber-level access and above, to send a test message via the Telegram Bot API to all users configured in the settings.