openssl command hangs

You need another argument, it expects to read a certificate from standard input. Probably you meant to add -new as a command line argument, or you need to pass an existing certificate on standard in.

I had the same issue when using GitBash in Windows 7, After hours of search this solved my issue:

winpty openssl genrsa -out ../private.pem -aes256 4096

Could give you some idea what is needed.