it needs re-seasoning again.
clean off the rust and dry it off, then half fill it up with Salt and heat it on medium/high for a good hour.
dump the salt out (not into anything that will melt, and then rub the inside of the pan with cooking oil, then just leave it to cool, wipe off the excess oil, and store that way.
harsh de-greasing detergents aren`t good for cast iron, you need to wipe a light oil coat on it after washing.
So long and Thanks for all the Fish ;)