Gather all ingredients. Preheat the oven to 325 degrees F (165 degrees C). Grease and flour a 10-inch Bundt or tube pan.

To make the cake: Sprinkle walnuts over the bottom of the prepared pan; set aside.

Mix cake mix, eggs, dark rum, water, oil, and vanilla pudding mix together in a large bowl until well combined. Pour batter over walnuts in the pan.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 1 hour.

Cool, then invert cake onto a serving plate. Gently prick holes into the top and sides of cake with a toothpick or skewer.

To make the glaze: Melt butter in a saucepan over medium heat. Stir sugar and water into melted butter; bring to a boil.

Cook, stirring constantly, for 5 minutes. Remove glaze from heat; stir in rum.

Drizzle warm glaze slowly over top and sides of cake, allowing the cake to soak up the liquid.