Can't tell what that is from the photo.
If the discoloration is on the outside edge of the humidor where the drawer fits, its possible that it's just a failed varnish coat and not mold. Mold is more likely to occur inside the humidor, near the humidifier where it is more moist then on the external seam of a door/drawer.
Generally speaking, the use of vinegar, bleach, detergent are all sure-fire ways to destroy the wood of the humidor or permanently taint it with an undesirable odor, or both.
If you have lowered the humidity, you can just wipe mold away. If you wish, you can use a bit of isopropyl alcohol or a mixture of ammonia and distilled water on a rag - just don't saturate the wood. This would increase the chances of ensuring that the colony is dead. Stains can be removed by a light sanding if desired, but this is not critical.
Unless you live in a salt mine, viable mold spores are everywhere in the air already, so your best method of control is to simply keep humidity in check.
