I know this is just a forum and the libs are always confused by nuance, but exploitation does occur in socialist countries, just in a vastly different character and at a much smaller scale. Cuba for instance does have private land owners who employee workers, and China of course has various large corporations.
However these are symptoms of the positions the nations find themselves within. Socialist nations tend to find themselves in the middle of capitalist encirclement. Until the last capitalist is extinguished, class based exploitation will continue to exist.