Which of the following is a protocol that is prone to a man-in-the-middle (MITM) attack...

Address Resolution Protocol (ARP) a stateless protocol was designed to map Internet Protocol addresses (IP) to their associated Media Access Control (MAC) addresses.

This being said, by mapping a 32 bit IP address to an associated 48 bit MAC address via attached Ethernet devices, a communication between local nodes can be made.

Source: (http://www.exploit-db.com/papers/13190/ )