This lab contains a blind OS command injection vulnerability in the feedback function.
The application executes a shell command containing the user-supplied details. The command is executed asynchronously and has no effect on the application's response. It is not possible to redirect output into a location that you can access. However, you can trigger out-of-band interactions with an external domain.
To solve the lab, exploit the blind OS command injection vulnerability to cause a DNS lookup to the public Burp Collaborator server (burpcollaborator.net).
The solution described here is sufficient simply to trigger a DNS lookup and so solve the lab. In a real-world situation, you would use Burp Collaborator client to verify that your payload had indeed triggered a DNS lookup. See the lab on blind OS command injection with out-of-band data exfiltration for an example of this.