In an attempt that reveals the greatest threat from a nuclear North Korea, a North Korean diplomat allegedly threatened an Israeli diplomat that, unless Israel paid North Korea $1 billion, it would sell ballistic missile technology to Iran. While this reportedly took place back in 1999, it highlights the proliferation threat of nuclear-armed Korea: while North Korea might be successfully deterred from using nuclear weapons themselves, any sale of weapons or weapons technology may go to organizations or governments who are more willing to use them or are high proliferation risks themselves. The threat of hidden weapons sales is especially great as the country suffers from heavy sanctions caused by their continued testing and development of weapons. 

Source: North Korea reportedly pushed $1 billion nuclear blackmail to Israel – Business Insider Deutschland