"Custom exploit" might be a bit of a misnomer, Billy and Terry (the same researchers that are credited on the initial ICS-CERT Advisory regarding the Niagara framework) were referencing a set of utilities/scripts they put together to automate testing.
Original ICS-CERT Advisory: http://ics-cert.us-cert.gov/advisories/ICSA-12-228-01
(Edit: Disclaimer, I work for Cylance.)