I don't agree. They have ballistic missiles. They have fairly advanced subs. They have nuclear weapons. They probably get sat intell from china or are able to hack it.
They could plant sleeping mines that are acoustically triggered. For all we know they have long range acoustic tracking torpedoes and sub-launched cruise missiles.
I know a carrier group will be protected by cruisers with sophisticated missile defense systems but they are not foolproof and can be overwhelmed by a volley of missiles. If they managed to somehow lob a nuke in the vicinity of the carrier task force, you can wipe them all off the board.
I don't know how to measure the threat, but it is not insignificant.
As military threats go, it's as close to insignificant as they come. Stratfor would tell you that an American carrier group is nigh impervious to even technologically advanced enemies like Russia. This isn't to say it can't be taken out. But NK has almost no chance of conventionally attacking a US carrier group with any chance of success.
You should read up on what goes into a carrier group's defense. You'd be rather surprised.
