Page Restrict <= 2.5.5 - Cross-Site Request Forgery via pr_admin_page

Description

The Page Restrict plugin for WordPress is vulnerable to Cross-Site Request Forgery in all versions up to, and including, 2.5.5. This is due to missing or incorrect nonce validation on the 'pr_admin_page' function. This makes it possible for unauthenticated attackers to modify the plugin's settings via a forged request granted they can trick a site administrator into performing an action such as clicking on a link.