From my dreams, I know that Ulfang is in a cave on the snowy northwestern edge of the Rivenwood.
He is in great danger.
I have devised a magical disguise that will make you appear as a worg while you are within the Rivenwood. The disguise is weak, relying upon the strange magics of that haunted wood. While it will only convince the worgs, it will allow you to get close to Ulfang.