Originally Posted by
MeVoy
I can't say if the RER is "safe" or not, but it does pass through some rather sketchy areas on its way into Paris.
Some RERs are direct to Gare Du Nord (stopping only at CDG1 en route). Not sure about late at night, however.
Although I would probably take a late night RER myself, I would feel uncomfortable recommending it to somebody else.
It may be worth your while considering staying overnight in a hotel near CDG and go to your final destination the next morning, assuming you do not already have a non-cancellable booking.