Funny that they warm this up again. Gorbachev had already admitted the existence of the secret part of the Hitler-Stalin-Treaty at the end of the USSR and the full text of the original treaty was published in 1993 by a Russian journal.
Before 1993, this secret treaty was part of German oral history, but only the Russians managed to locate an existing original of it, while the German one was destroyed by the bombing of the Reichskanzlei. Copys of it already circulated through Europe since 1939, but those had been considered fake in the USSR.
Also, the treaty was already highly embarrassing for the USSR right after World War 2. During the Nuremburg trials, they fought hard against any mentioning of such a treaty by Nazi officials, like Ernst von Weizsäcker.