Donation Button <= 4.0.0 - Subscriber+ Broken Access Control leading to SMS Spam

The Donation Button WordPress plugin through 4.0.0 does not properly check for privileges and nonce tokens in its "donation_button_twilio_send_test_sms" AJAX action, which may allow any users with an account on the affected site, like subscribers, to use the plugin's Twilio integration to send SMSes to arbitrary phone numbers.