What are my responsibilities as a car lease co-signer in case a car accident and lack of insurance liability?

I'm a co-lesse in a car lease. A primary lesse have had a car accident where several cars were involved. An insurance coveridge for property damage and bodily injury liability is short to pay full amount of money for this accident. Do I have to pay my personal money to cover lack of liability in this case or this is responsibility of the primary lessee only?