faces/context/PartialViewContextImpl.java in Eclipse Mojarra, as used in Mojarra for Eclipse EE4J before 2.3.10 and Mojarra JavaServer Faces before 2.2.20, allows Reflected XSS because a client window field is mishandled.
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.