A 4.8v reading on a loose pin 0?
If it's set as an input pin then trying to measure the voltage on it is largely unproductive unless, of course you believe it may be still set as an output - then you would need to attach a load to it to see if the voltage it is producing is "real" or just some leakage current from an unconnected input making a high impedance voltmeter show something like 4.8V.

Try connecting a 1k resistor to ground from this pin - does it still show logic 1 or perhaps it's now at logic 0.

Some IO pins will default (on some MCUs) to having an inbuilt high resistance pull-up of the order 100k and this may also be happening. This (on some MCUs) can be programmed to be (a) not there at all, (b) pull-up or (c) pull-down. I believe some MCUs can program a lower resistance or a higher resistance. Maybe this is also happening?