Preheat oven to 300 degrees F (150 degrees C). Grease 14 muffin cups.
Lightly beat bananas and white sugar together in a bowl until smooth; add eggs, one at a time, until incorporated. Beat in vegetable oil until well blended, 1 to 2 minutes. Stir in flour, baking soda, and buttermilk; mix well. Fold in pecans. Pour batter into the prepared muffin cups.
Bake in the preheated oven until a toothpick inserted in the center of a cupcake comes out clean, 20 to 30 minutes. Sprinkle cupcakes with confectioners’ sugar.