Set to 350°F (175°C). Grease and flour a 9x13-inch pan or two 8-inch round pans.
In a large bowl, beat cake mix, milk, oil, eggs, mashed strawberries, and vanilla on medium speed for 2–3 minutes until smooth.
Pour into prepared pan(s) and bake for 28–32 minutes, or until a toothpick comes out clean.
While baking, whisk together powdered sugar, pureed strawberries, melted butter, vanilla, and salt until smooth.
Cool cake in pan for 10 minutes, then transfer to a wire rack. While still warm, pour glaze over the top and let it drip down the sides.