Ultra Skype Button <= 1.0 - Authenticated (Contributor+) Stored Cross-Site Scripting via 'btn_id' Shortcode Attribute

The Ultra Skype Button plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'btn_id' parameter of the [ultra_skype] shortcode in all versions up to, and including, 1.0 due to insufficient input sanitization and output escaping. 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.