This can be fixed. You need to get CA glue that is really thin. You can buy it at hobby stores like Hobby Lobby. Mask off the area around the cracks with tape. String the bow so the cracks will open up. If this does not open the cracks, find a way to do so, such as torquing the riser to open the cracks. Once you have opened the cracks slowly fill the crack with the CA. Because the CA is so thin, it will soak into the wood. Keep adding CA until the wood will not absorb anymore. At that point unstring the bow so the cracks will close. You may need to apply pressure with clamps. Let the bow set overnight and it should be fixed. I had a bow that crack through the sight window into the grip due to a dry fire. I used this technique and have had to additional issues. If you want to go one step further, you could drill a hole perpendicular to the cracks and thread a wood or dry wall screw into the hole. Back the screw out all the way and score it with a pair of pliers. Add CA to the screw and run it back into the wood until the scored area of the screw is just below the surface of the wood. Now slowly bend the head of the screw back and forth until the screw breaks off. The screw should now be below the surface of the wood. If you have any scrap would from when the riser was made, sand it and mix the dust with 5 minute epoxy to make a paste that will match the riser. Now fill the hole, allow to cure completely, sand and spray with whatever finish you like. If you have any questions, please let me know.