The first thing that the risk practitioner should do upon learning that a new third-party system on the corporate network has introduced vulnerabilities that could compromise corporate IT systems is to notify information security management. This will help to escalate the issue to the appropriate authority and responsibility level, and to initiate the incident response process. Information security management can also coordinate with the third party, the IT department, and other stakeholders to assess the impact and severity of the vulnerabilities, and to implement the necessary actions to contain, eradicate, and recover from the incident. Confirming the vulnerabilities with the third party, identifying procedures to mitigate the vulnerabilities, and requesting IT to remove the system from the network are not the first things that the risk practitioner should do, as they may not address the urgency and priority of the issue, and may not involve the relevant decision makers and responders. References = Risk and Information Systems Control Study Manual, 7th Edition, Chapter 4, Section 4.2.1.2, page 1931

1: ISACA Certified in Risk and Information Systems Control (CRISC®) Exam Guide, Answer to Question 659.