If you are buying an HDB flat
You can use your CPF savings to buy an HDB flat or pay the housing loan of your existing HDB flat, provided you are the owner of the HDB flat. You will need to contact HDB directly regarding this matter.
If you are buying a private property
You will need to obtain consent from the Official Assignee before you can use your CPF savings to buy a private property or pay the housing loan of your existing property.