If the finish is just dull and not compromised buffing out with paste wax is your best option.
You will probably not get the high gloss sheen back but it will look good.
If the finish is compromised you are better off sanding it and re-finishing with either a exterior urathane or marine varnish.
The other option if you really want the high gloss back and the existing finish is intact is to scuff the cabinet with 320 grit sand paper and
recoat with one of the above finishes.If you go that route make sure you do a small area on the back of one of the doors just to make sure you do not get a reaction.
Not all finishes are compatable and may turn into a mess not likely but possable