I tried to use the -subj parameter and used "test-intern" as Common Name.
The module interprets the "-in" as new parameter and not as string.

Example throwing an error:

global.openssl(['req', '-config', {name: "csr.conf", buffer: csrConfigBuffer}, '-new', '-key', {name: "private.pem", buffer: privateKeyBuffer}, "-subj", "/C=Test/ST=Test/L=Test/O=Test/OU=Test/CN=test-intern"], function(errorOutput, bufferOuptut) {

Resolved by changing:

const checkCommandForIO = element => element.includes('-in') || element.includes('-out')
    || element.includes('-keyout') || element.includes('-signkey') || element.includes('-key')

to:

const checkCommandForIO = element => element == '-in' || element == '-out'
    || element == '-keyout' || element == '-signkey' || element == '-key'  || element == '-config'