Mstoic Shortcodes <= 2.0 - Authenticated (Contributor+) Stored Cross-Site Scripting via 'start' Shortcode Attribute

The Mstoic Shortcodes plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'start' parameter of the ms_youtube_embeds shortcode in all versions up to, and including, 2.0 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.