Bug affected a Steam API and was patched in August. Downgrading your Steam client won’t help you get free games.
November 8th, 2018, By Catalin Cimpanu
Ukrainian vulnerability researcher has found a bug that would have allowed him to download all the activation keys (also known as CD keys) made available through the Steam gaming platform, for any game, ever.
Discovered by Artem Moskowsky, the bug resided in Steamworks, a platform that Valve runs to help developers with building and publishing games via its Steam gaming client.
Moskowsky found the bug in a Steam web API located at partner.steamgames.com/partnercdkeys/assignkeys/.
This is the API that lets game developers or affiliates retrieve CD keys made available to Steam users so their customers can activate a game installed via the Steam client.