Responsive Blocks < 2.2.1 - Unauthenticated Open Email Relay via REST API 'email_to' Parameter

Description

The plugin is vulnerable to Unauthenticated Open Email Relay due to insufficient authorization checks and missing server-side validation of the recipient email address supplied via a public REST API route. This makes it possible for unauthenticated attackers to send arbitrary emails to any recipient of their choosing through the affected WordPress site's mail server, effectively turning the site into an open mail relay.