Flat UI Button <= 1.0 - Authenticated (Contributor+) Stored Cross-Site Scripting via flatbtn Shortcode

The Flat UI Button plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin's flatbtn shortcode in version 1.0 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.