Really? There’s nothing in the Wiki to show plans were stolen.
However, the Ilyushin Il-2 (and later the Ilyushin 10) pioneered almost all of the characteristics of the YA-9 and YA-10. Other than the jet engines and inability to carry heavy bomb loads, the thievery could almost be said to be in the other direction - or that similar missions require similar designs.
https://en.wikipedia.org/wiki/Ilyushin_Il-2
Does not seem to me that there was any need to steal anything; the Russians are really good at designing planes - manufacture is an other story.