The Sticky plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the `cvmh-sticky` shortcode `readmoretext` attribute in versions up to and including 2.5.6. This is due to insufficient input sanitization and output escaping in the `cvmh_sticky_front_render()` function — the `readmoretext` attribute value is passed through `apply_filters()` and directly concatenated into the HTML output without any escaping function such as `esc_html()`. 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 a page containing the injected shortcode.
https://plugins.trac.wordpress.org/browser/sticky/trunk/includes/shortcode.php#L7
https://plugins.trac.wordpress.org/browser/sticky/trunk/includes/functions.php#L118
https://plugins.trac.wordpress.org/browser/sticky/tags/2.5.6/includes/shortcode.php#L7
https://plugins.trac.wordpress.org/browser/sticky/tags/2.5.6/includes/functions.php#L118