If the faucet leaks from underneath and you can verify that it is not the flex lines or the drain line leaking it could be a sign that you will need a new faucet. Changing the cartridge or the faucet stem can sometimes remedy the leak from underneath if you want to try to repair it. A faucet repair is less expensive and less time consuming, so if you like your faucet then you can try to repair it before you go through the process of replacing it.
Note: For a newer faucet that is leaking from any of these areas the first thing to do is to check the warranty and contact the manufacturer. Many manufacturers have lifetime warranties on faucet leaks. They can send you the parts you will need to repair your faucet or if it is a faulty faucet they may even send you a new faucet.