They are working on putting ballistic missiles on a sub, currently they only have road mobile ICBMs that can reach much of the USA with nukes.
(Also, I hope you remember that they've got nukes now, partly courtesy of US domestic politics counting above mitigating real world problems)
No doubt the North Koreans still have a lot left before reaching the operational capability of the Russian road mobile ICBM forces, particularly with respect to accuracy and reliability. But nuclear weapons are not that picky with aiming, and numerical redundancy is certainly within the North Korean capability.