Falling to Corruption

The aggression of the Winterfall furbolg has to have its source somewhere. I'd like to get to the bottom of it if I can! I've seen the furbolg in the camps to the north brewing something in a cauldron. They seemed very protective of it... if whatever they're cooking up is what's causing this, I must examine it myself. Find that cauldron if it's still there, and bring me back what's inside!