The recent dependency on concurrent-output adding implies downloading, compiling, and executing as root of many (MissingH, hslogger, process, unix-compat, network, directory, ansi-terminal, unix, ...) unstrusted sources. This seems like a huge security problem...
Are these at least downloaded using https?
Yes, cabal is not secure from MITM.
I've rethought adding that dependency so soon. I'll change back to bundling concurrent-output in 3.0.1.
I can force ghc to build the concurrent-output module with -O2 as needed to get good memory use, and still let the rest of propellor build with -O0, which was the main motivation for unbundling it.