Input validation vulnerability in Sign-up Sheets 2.2.11.1

The Sign-up Sheets plugin on WordPress has a security issue called Cross-Site Request Forgery. This affects versions 2.2.11.1 and below. The problem is that a certain function does not properly check for a special code that helps prevent unauthorized actions. Because of this, attackers who are not logged in can trick a website administrator into doing something they should not be able to do. This can happen if the administrator clicks on a fake link.