ARP Poisoning

Arp Poisoning
also known as ARP Poison Routing, is a network attack that exploits the transition from Layer 3 to Layer 2 addresses.

ARP (address resolution protocol) operates by broadcasting a message across a network, to determine the Layer 2 address (MAC address) of a host with a predefined Layer 3 address (IP address). The host at the destination IP address sends a reply packet containing its MAC address. Once the initial ARP transaction is complete, the originating device then caches the ARP response, which is used within the Layer 2 header of packets that are sent to a specified IP address. 

An ARP Spoofing attack is the egression of unsolicited ARP messages. These ARP messages contain the IP address of a network resource, such as the default gateway, or a DNS server, and replaces the MAC address for the corresponding network resource with its own MAC address. Network devices, by design, overwrite any existing ARP information in conjunction with the IP address, with the new, counterfeit ARP information. The attacker then takes the role of man in the middle; any traffic destined for the legitimate resource is sent through the attacking system. As this attack occurs on the lower levels of the OSI model, the end-user is oblivious to the attack occurrence.

ARP Poisoning is also capable of executing Denial of Service (DoS) attacks. The attacking system, instead of posing as a gateway and performing a man in the middle attack, can instead simply drop the packets, causing the clients to be denied service to the attacked network resource. The spoofing of ARP messages is the tributary principal of ARP Poisoning.

Attack Vector

Ettercap is a suite for man in the middle attacks on LAN. It features sniffing of live connections, content filtering on the fly and many other interesting tricks. It supports active and passive dissection of many protocols (even ciphered ones) and includes many feature for network and host analysis.
Arpspoof is a tool that can send fake arp reply in network in one go.Its a small and a very powerful tool.

Arp Poisoning

Above figure show the scenario over which we will be performing arp poisoning using ettercap and arpspoof tools.

Attack:

Step 1:In this step we first look for ipv4 address and MAC address of victim.

Step 2:Now here we will launch our attack by firing ettercap in command mode.

 Same can be done using arpspoof as shown below:

Step 3:See in host list of ettercap that whether the victim is added as a target for arpspoofing or not.

Step 4:Now victim is poisoned as you can see in figure that gateway MAC is same as of attacker’s machine MAC.

Step  5:Do another little check to make sure that  data is going through victim to gateway.

To make Our attacker machine a router so that he can pass the data requested by victim to the victim which attacker will receive from gateway by acting as a man in middle we have to run following command in attacker machine so that he can forward packets.

echo 1 > /proc/sys/net/ipv4/ip_forward

Mitigation:
Mitigation of ARP Poisoning can be performed on the Cisco IOS with DAI (DYNAMIC ARP INSPECTION) which is relying on DHCP Snooping. Enable DAI

ip arp inspection vlan <Vlan ID>
Enable DHCP snooping