The WP Responsive Popup + Optin plugin for WordPress is vulnerable to Cross-Site Request Forgery in all versions up to and including 1.4. This is due to the settings form on the admin page (wpo_admin_page.php) lacking nonce generation (wp_nonce_field) and verification (wp_verify_nonce/check_admin_referer). This makes it possible for unauthenticated attackers to update all plugin settings including the 'wpo_image_url' parameter via a forged request, granted they can trick a site administrator into performing an action such as clicking a link.