Input validation vulnerability in MailUp Auto Subscription 1.1.0

The MailUp Auto Subscription plugin for WordPress has a security issue that makes it vulnerable to attacks. This can happen in all versions up to and including 1.1.0. The problem is that the plugin does not properly check for forged requests, which allows attackers to change settings and insert harmful code into the website. They can do this by tricking a site administrator into clicking on a link.