The Joli Table Of Contents WordPress plugin before 3.0.3 does not sanitise or escape a shortcode attribute value before outputting it inside an HTML element's attribute, allowing users with the Author role and above to inject arbitrary HTML attributes and JavaScript that execute in the browser of any user who views the post, including higher-privileged users such as administrators. This crosses a privilege boundary even on multisite, where such users are not permitted to post unfiltered HTML.