The script says it's a rewrite of metasploits implementation:
https://github.com/rapid7/metasploit-framework/blob/master/modules/auxiliary/scanner/ipmi/ipmi_cipher_zero.rb

However there is a bug: The servers response code, whether the connection was accepted or not is not checked.
Therefore current version of nmap ipmi-cipher-zero reports false positives for all ipmi services that respond to a request to open connection with cipher zero, even if the response was to deny the connection.

This pull request fixes that.