It’s great that there is one office of Vietnam embassy in Havana, Cuba.
Vietnam’s embassy in Havana is the only Vietnamese representation in Cuba up to now. This office provides services of visa issuance and consular legalization among others, and also the place that Vietnamese citizens in Cuba should contact immediately if they lose their passport.
Regarding visa for Vietnam, in addition to embassy visa, citizens and residents of Cuba has an alternative of getting a visa on arrival. You can see their brief below:
For details, you may also read: