Preheat oven to 350 degrees. Spray a non-stick bundt cake pan with cooking spray.
Add the cake mix, water, eggs, and oil to the bowl of a stand mixer. Beat on high, stopping to scrape down the sides of the bowl once, until batter is very smooth (2 - 3 minutes).
Mix together the graham cracker crumbs, brown sugar, melted butter and salt. Stir the graham mixture into the cake batter.
Pour the batter into the pan and smooth the top. Bake for 35 - 40 minutes, or until the top of the cake springs back when lightly touched.
Allow the cake to cool in the pan for about 15 minutes. Remove from pan and allow to cool completely.
When ready to serve the cake, drizzle with about half of the hot fudge sauce. Serve the rest of the sauce with the cake.