Apparently they may have gotten a massive boost in their capabilities from a Ukranian missile plant that used to make the Soviet Union/Russian Federation's ICBM's

https://www.nytimes.com/2017/08/14/w...e-factory.html

Analysts who studied photographs of the North’s leader, Kim Jong-un, inspecting the new rocket motors concluded that they derive from designs that once powered the Soviet Union’s missile fleet. The engines were so powerful that a single missile could hurl 10 thermonuclear warheads between continents.

Those engines were linked to only a few former Soviet sites. Government investigators and experts have focused their inquiries on a missile factory in Dnipro, Ukraine, on the edge of the territory where Russia is fighting a low-level war to break off part of Ukraine. During the Cold War, the factory made the deadliest missiles in the Soviet arsenal, including the giant SS-18. It remained one of Russia’s primary producers of missiles even after Ukraine gained independence.
Further in the article:

Bolstering his conclusion, he added, was a finding by United Nations investigators that North Korea tried six years ago to steal missile secrets from the Ukrainian complex. Two North Koreans were caught, and a U.N. report said the information they tried to steal was focused on advanced “missile systems, liquid-propellant engines, spacecraft and missile fuel supply systems.”
So maybe everyone should really consider that this foot loop has or will have very shortly, real missiles and likely other tech to drop nukes on the US or the rest of the world. Amazing how ignoring Putin's little war of conquest in Ukraine and basically blocking the Ukraine from joining Nato is going to bite us in the ass.