There is a Cross-site Scripting vulnerability in Portal for ArcGIS in versions 11.2 and below that may allow a remote, authenticated attacker to provide input that is not sanitized properly and is rendered in error messages. The are no privileges required to execute this attack.
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.