The X server allows an X client to:

 - Snoop on the screen by reading its contents.
 - Snoop on the keyboard.
 - Take control of other X clients by sending them keyboard and mouse events.
 - Impersonate other X clients by using their names in window title bars.
 - Discover what other X clients are running.
 - Steal the input focus.
 - Deny service by grabbing the pointer or keyboard or the whole server.
 - Deny service by consuming the X server's resources. strong text