Final answer:
ARP, or Address Resolution Protocol, is exploited to achieve an on-path position, allowing attackers to intercept traffic in a man-in-the-middle attack through ARP poisoning or ARP spoofing.
Step-by-step explanation:
The protocol that is exploited to achieve an on-path position is ARP (Address Resolution Protocol). The ARP protocol is used to map an IP address to a physical machine address that is recognized in the local network. An attacker can manipulate ARP messages on the network to link their MAC address with the IP address of another host, such as the default gateway, causing all the traffic meant for that IP to pass through the attacker's device.
This technique is known as ARP poisoning or ARP spoofing and is a common method to perform a man-in-the-middle attack.