Preheat oven to 350 degrees F.
Spray a 9x13" baking dish with cooking spray. Optional, but recommended: line dish with parchment paper.
Prepare brownie mix according to package directions.
In a separate bowl, beat together the butter, brown sugar, granulated sugar, vanilla, and pumpkin puree.
Add the flour, spices, baking soda, and salt, and mix until well combined.