There is a reflected cross site scripting in Esri Portal for ArcGIS 11.1 and below on Windows and Linux x64 allows a remote authenticated attacker with administrative access to supply a crafted string which could potentially execute arbitrary JavaScript code in the their own browser (Self XSS). A user cannot be phished into clicking a link to execute code.
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.