This happens when the carpet is wet either by spilled drinks or cleaning without separating the furniture from the wetness. Most furniture has plastic on the bottom of the feet to help prevent this, but for stained wood that is in direct contact with moist carpet this is usually the result. Unfortunately, there’s not much you can do to treat and reverse Stain Transfer. Best remedy is to be cognizant of these type situations before they develop. To protect areas that may have a high potential for wet carpet you might want to consider using furniture sliders underneath the feet. If there is an immediate need and if you can’t move the furniture from the area, in a pinch you could use sandwich bags or cut up a plastic trash bag, just some kind of barrier to separate from the wetness. Options to resolve this type of stain usually involves a discussion about carpet repair like exchanging plugs of carpet from a closet.