The Mailgun for WordPress plugin before 2.2.1 does not perform any capability or nonce check on an unauthenticated AJAX action that adds subscribers to the site owners configured email service mailing lists, allowing unauthenticated attackers to enrol arbitrary email addresses into those lists using the owners stored API credentials.
The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.
Access control involves the use of several protection mechanisms such as:
When any mechanism is not applied or otherwise fails, attackers can compromise the security of the product by gaining privileges, reading sensitive information, executing commands, evading detection, etc. There are two distinct behaviors that can introduce access control weaknesses: