The Simple Banner plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the `pro_version_activation_code` parameter in versions up to, and including, 2.11.0 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, including those without administrative capabilities when access is granted to those users, to inject arbitrary web scripts in page that will execute whenever a user role having access to "Simple Banner" accesses the plugin's settings.