There is a period during the house buying process where you may be cleared to close, but the loan may still be denied. This is called the cleared to close phase, which signifies the approach of the closing date, but the lender still needs to finalize the loan paperwork. So, if the lender rechecks your credit and your circumstances have changed, the loan may be denied.
However, once you have signed your loan documents and closed on the deal, it is legally binding.