Simple Popup Plugin <= 4.5 - Authenticated (Contributor+) Stored Cross-Site Scripting

The Simple Popup Plugin plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin's [popup] shortcode in all versions up to, and including, 4.5 due to insufficient input sanitization and output escaping on user supplied attributes. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.