The vCenter Perfcharts service cookies must have "http-only" flag set.
Cookies are a common way to save session state over the HTTP(S) protocol. If attackers can compromise session data stored in a cookie, they are better able to launch an attack against the server and its applications. When a cookie is tagged with the "HttpOnly" flag, it tells the browser this particular cookie should only be accessed by the originating server. Any attempt to access the cookie from client script is strictly forbidden.