Preheat the oven to 350 degrees F (175 degrees C). Grease 12 muffin cups or line with paper liners.

Mash bananas and sugar together in a bowl; add egg and vanilla and mix well. Combine flour, baking powder, baking soda, and salt together in a separate bowl. Stir into banana mixture just until batter is mixed. Stir oil into batter and fold in cranberries. Spoon batter into the prepared muffin cups.

Bake in the preheated oven until a toothpick inserted in the center comes out clean, 22 to 26 minutes.