ARP Spoofing Explained: How Attackers Hijack Network Traffic

 ARP Poisoning

ARP poisoning (also known as ARP spoofing) is a type of cyberattack that exploits the Address Resolution Protocol (ARP), which is used to map IP addresses to MAC (Media Access Control) addresses in a local network. Here's a detailed breakdown of how it works, why it's dangerous, and how it's mitigated:

How ARP Works

In a local network:

• Devices communicate using IP addresses.
• To send data to another device, the sender needs the recipient's MAC address.
• ARP resolves this by sending a broadcast message like:
• "Who has IP 192.168.1.1? Tell 192.168.1.100"
• The device with that IP replies with its MAC address.
• The sender stores this mapping in its ARP cache.

What Is ARP Poisoning?

ARP poisoning is when an attacker sends fake ARP messages to a network. These messages falsely associate the attacker's MAC address with the IP address of another device (like the gateway or another host).

Example:

• Attacker sends a spoofed ARP reply:
• "192.168.1.1 is at AA:AA:AA:AA:AA:AA" (attacker’s MAC)
• Victim updates its ARP cache with this incorrect mapping.
• Now, traffic meant for 192.168.1.1 goes to the attacker.

Goals of ARP Poisoning

1. Man-in-the-Middle (MitM) Attack

• Attacker intercepts and possibly alters communication between two devices.

2. Data Theft

• Sensitive information like login credentials can be captured.

Session Hijacking

• An attacker can take over active sessions.

Denial of Service (DoS)

• Redirecting traffic to a non-existent MAC address can disrupt communication.

How It’s Done

Attackers use tools like:

• Ettercap
• Cain & Abel
• BetterCAP
• arpspoof

These tools automate the sending of spoofed ARP packets to poison caches across the network.

Detection and Prevention

Detection

• Unusual ARP traffic or frequent ARP replies.
• Duplicate IP addresses with different MACs.
• Tools like:
• Wireshark (packet analysis)
• ARPwatch (monitoring ARP activity)

Prevention

1. Static ARP Entries

• Manually configure IP-MAC mappings (not scalable).

2. Packet Filtering

• Use firewalls to block spoofed packets.

3. Encryption

• Use HTTPS and VPNs to protect data even if intercepted.

4. Network Segmentation

• Limit broadcast domains.

5. Dynamic ARP Inspection (DAI)

• Available on managed switches; validates ARP packets against the DHCP snooping database.