Avishi WP PayPal Payment Button <= 2.0 - Cross-Site Request Forgery to Stored Cross-Site Scripting

The Avishi WP PayPal Payment Button plugin for WordPress is vulnerable to Cross-Site Request Forgery in all versions up to, and including, 2.0. This is due to missing or incorrect nonce validation on the 'avishi-wp-paypal-payment-button/index.php' page. This makes it possible for unauthenticated attackers to update settings and inject malicious web scripts via a forged request granted they can trick a site administrator into performing an action such as clicking on a link.