Mix sawdust or wood shavings with a small amount of wood glue until they form a thick paste. The paste should be spreadable and not run.
Press the paste into the crack using a flexible plastic putty knife. Angle the putty knife slightly to scrape away the excess paste from the top of the repaired area as well as from the outer edges. Allow the paste to dry, and sand the area with 100-grit sandpaper until the surface is even.
Apply a thin layer of wood filler using the plastic putty knife. This time, apply the filler over the crack as well as the surrounding area. Smooth the wood filler on the cabinet's surface, keeping it as even as possible. Allow the wood filler to dry, and sand the area smooth with 100-grit sandpaper.
Smooth the repaired area with a 150-grit sanding block to roughen the surface slightly.
Paint or stain the cabinet as usual to cover the patch.