If we can trust wiki, in addition to old Soviet-made stuff, they possess Buk SAMs which are quite capable, but short-range (~30 km max)And btw, do you think NK has not mobile SAMs and AA? Add to that fixed SAM sites near the frontier which may have enough range to cover until Seoul airspace. NK have inverted lots of resources in getting modern air defenses.
Also Igla manpads, which are dangerous for helicopters and ground attack aircraft.
It looks like there are no reliable data about their real capabilities though.