One problem with Cabal is that it pulls packages from Hackage, and as it's been discussed some time ago, there are many ways how a piece of malicious code can get in.
Does Stack improve the situation and does it take any precautions against that? Is it possible to make sure that all code downloaded externally for a given project is verified?
This includes extra dependencies - if there are any declared, is it possible to let stack verify them, for example to give an expected hash of the downloaded package?