The WP Dropzone plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'callback' shortcode attribute in all versions up to, and including, 1.1.1. This is due to insufficient input sanitization and output escaping on user-supplied 'callback' attributes, which are evaluated as JavaScript code via the `new Function()` constructor. 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.