A recent military parade in North Korea featured the first public appearance of the long rumored RSM-25 (or Musudan) missile. This is a variant of the Russian SS-N-6 submarine launched missile. The North Korean version is believed to weigh 20 tons and have a range of over 3,000 kilometers. But there have been no tests, so it's uncertain if the North Koreans have been able to make the Russian design work for them.
The SS-N-6 is a 1960s vintage ballistic missile, and is known in Russia as the R-27. SS-N-6 is a NATO code name for the R-27. This was Russia's first true submarine launched ballistic missile (SLBM), and sixteen of them were carried in Yankee class SSBNs (missile carrying nuclear submarines.) The 12 ton R-27 had a range of 2,800 kilometers and uses storable liquid fuel. This means it can be ready for launch in less than half an hour.
After the R-27 was replaced by more modern missiles in the 1970s, the missile continued to be used for scientific research until 1990. By that time, 492 R-27s had been launched, 87 percent of them successfully.
It would be very embarrassing for the Russians if someone had illegally exported SS-N-6/R-27 missiles to North Korea. It is more likely, and was been reported a few years ago, that the Russian organization that designed the R-27, had illegally sold the plans to North Korea. This was supposed to have happened sometime in the 1990s, and the main reason for the deal was so that North Korea could obtain the R-27 missile guidance technology. The Russians kept improving the guidance system of the R-27 through the 1980s, while the North Koreans were desperate for missile guidance technology. But it appears that the North Koreans built at least one R-27, and may have incorporated R-27 technology in some of their other long range ballistic missiles.