The contact owns a 2020 Chevrolet Blazer. The contact stated that after driving into the garage, the engine was turned off but the transmission was left in the drive position. The contact mentioned that the brake was intended to engage in order for the vehicle not to move forward or backward. After exiting the vehicle moments later the vehicle began to roll backward out of the garage. The contact immediately attempted to stop the vehicle from rolling into the neighbor's home by grabbing the driver's side mirror. The contact was able to prevent the crash from occurring but in the process had sustained injuries to the left shoulder, neck, and back and both the left and right hip and knees which required medical treatment. The cause of the failure was not determined. The local dealer was notified of the incident but no assistance was offered. The manufacturer was not notified. The failure mileage was 4,400