The hk_shortcode plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'title-plane' shortcode in versions up to, and including, 1.0. This is due to insufficient input sanitization and output escaping on user-supplied shortcode attributes in the huankong_post_short_title_plane() function, where the 'title' attribute is concatenated directly into HTML output without any 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.