Input validation vulnerability in Page Restrict 2.2.2

The Page Restrict plugin for WordPress is vulnerable to a security issue. Attackers who have admin level permissions can inject malicious code into a page, which will be executed when a user visits the page. This can be done via Cross-Site Request Forgery. The vulnerable versions of the plugin are up to, and including, 2.2.1. To protect against this, input sanitization and output escaping should be done.