They would be violating the "big" treaty if they had not pulled out of it. It doesnt make sense to say they aren't in violation to a treaty they no longer wish to follow. (and they didnt follow it even when they were party to it)
But they are a part of the U.N. which has banned them with repeated resolutions. The
main one being:
October 14, 2006:
The UN Security Council adopts Resolution 1718. The measure demands that North Korea refrain from further nuclear tests and calls on Pyongyang to return to the six-party talks and abandon its nuclear weapons. It also imposes additional sanctions on commerce with Pyongyang, widening the range of prohibited transactions beyond those banned under Resolution 1695.