South Korea and Bangladesh have signed agreements to increase defense cooperation. South Korea sees Bangladesh as a customer for the growing number of South Korea made weapons available for export. But the new military agreements are only a small part of the new deals, most of which involve economic cooperation. Bangladesh wants more South Korean investment, to aid economic development. This (along with lower tariffs for Bangladeshi exports to South Korea) helps close the trade imbalance with South Korea.
There are also new military exchange agreements. There are about 130,000 Bangladeshis working in South Korea, most of them there illegally. But this is not seen as a security problem, as Bangladesh has stayed on top of its Islamic radical problem, and there have been few such problems in South Korea.