Hi this is Peggy. Here are some instructions on fixing you cracked MDF so it will support screws. Good luck How to Repair Cracked MDF | Home Guides | SF Gate
Consequently, repairing cracked MDF is usually a simple matter. ... repairs, you should use one with structural strength if the repair has to hold screws or nails.
Missing: support | Must include:
I would use wood filler.
You could try gluing it with a gorilla glue or a P900 contractor's glue. MDF is a very soft product, not as good as plywood, so you may have to support the location you are drilling with a backing of a stud. Not sure what your project is..
Thanks everyone! I suspected I need to support the mdf with a piece of wood (after gluing crack) and you all have helped!