Can non-custodial parent be held responsible?

What is the name of your state (only U.S. law)? California
My son lives with his dad (he has physical custody, we have joint legal custody), my ex doesn't have a driver's license and recently he bought our 17 yr old a car. My son doesn't have a permit (because his dad can't get him one because he's not licensed and didn't want me to). My concern is if my son is in an accident can I be held financially responsible. I can't control either of them. But i don't want to be left holding the bag if something happens.What is the name of your state (only U.S. law)?

It's theoretically possible, as long as he is under 18, that you could be named in a suit.

He won't even be able to get insurance if he doesn't have a license. What is dad thinking??? He could DEFINITELY be held responsible!