This is a much bigger problem than just Counter Strike. I'm pretty confident there are 1000+ games on the steam store that have vulnerabilities where a simple link or network packet while gaming can exploit a user's machine.
Both MS and Steam really need to work on locking down Windows.
MS already did that. UWP apps are sandboxed. They even recently made an OpenGL implementation over DirectX 12 (vendor implementations are incompatible with UWP sandbox).
A few games in Microsoft Store are actually properly sandboxed as the result. For example, We Happy Few.
Both MS and Steam really need to work on locking down Windows.