The Master Slider – Responsive Touch Slider plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin's 'ms_layer' shortcode in all versions up to, and including, 3.9.10 due to insufficient input sanitization and output escaping on the 'css_id' user supplied attribute. 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.