Swift SMTP < 5.0.7 - Cross-Site Request Forgery

Description

The Swift SMTP (formerly Welcome Email Editor) plugin for WordPress is vulnerable to Cross-Site Request Forgery in all versions up to, and including, 5.0.6. This is due to missing or incorrect nonce validation on the ajax_handler() function. This makes it possible for unauthenticated attackers to send emails via a forged request granted they can trick a site administrator into performing an action such as clicking on a link.