Preheat the oven to 350°F (180°C). Lightly grease an 11x7-inch baking dish.

Mix cake mix, melted butter, eggs, and 1 teaspoon vanilla extract in a bowl until well combined. Spread mixture into an even layer in the prepared baking dish.

Bake in the preheated oven until a toothpick comes out clean when inserted into the center, about 16 to 18 minutes. Allow brownies to cool in the pan for about 20 minutes.

Meanwhile, puree strawberries and remaining teaspoon of vanilla extract in a food processor or with an immersion blender until smooth.

Stir strawberry mixture into confectioner's sugar until smooth, adding extra sugar as necessary to reach the consistency of a glaze. Add salt and stir.