What is ARP Spoofing and How to Prevent it?

ARP spoofing is a type of cyberattack in which the hacker sends out a false Address Resolution Protocol (ARP) message over a Local Area Network (LAN).

In this article, we’ll take a look at ARP spoofing, or ARP poisoning, what is it, how it works, how you can detect ARP spoofing attacks and finally, how to prevent an attack on the ARP protocol.

So let’s get started.

What is ARP (Address Resolution Protocol)?

Before we can fully understand ARP spoofing, we need to understand ARP protocol first.

APR Protocol is responsible for translating a MAC address into an Internet Protocol address and vice versa.

In other words, the Address Resolution Protocol enables your computer or another device to contact the router and connect to the network (Internet). Here, a host maintains an ARP cache, or a mapping table. This ARP table is called on every time IP data packets are sent between hosts on a LAN, which enables better connections between network destinations.

What happens if an IP address is not known to the host?

In this case, an ARP request is sent, meaning a broadcast packet. If a computer with that IP address exists (and is connected to the network), it replies with its Media Access Control (MAC) address before it gets added to the cache.

What are ARP Spoofing Attacks?

Several issues make ARP less than secure.

• ARP protocol lacks any sort of verification to confirm that the request originates from an authorized user. This is what primarily enables ARP spoofing attacks;
• When a new ARP reply is received, old, unexpired ARP entries become overwritten;
• Even if no ARP request is sent, hosts will cache replies since ARP is a stateless protocol;
• ARP only works with IPv4 and on 32-bit IP addresses.

Okay, so what is ARP spoofing or ARP poisoning?

It’s a type of malicious attack in which the cyberattacker tricks the default gateway to relate their MAC address to the victim’s IP address by sending out ARP packets to the gateway on the local area network (LAN).

What is ARP Spoofing Usually Used For?

On its own, ARP spoofing might not be that big of a deal. Instead, it usually serves as a vanguard for more sophisticated types of attacks such as:

• Man-in-the-middle attacks – The attacker intercept and tweaks the traffic between the sender and the recipient. Read more about MITM attacks;
• DDoS attacks – ARP spoofing allows the cybercriminal to use the MAC address of the server they want to attack and not their own and to launch a DDoS attack. He can then repeat that for as many IP addresses as he needs to flood the traffic;
• Session hijacking – ARP spoofing also allows the hacker to get the victim’s session ID and access accounts that the target has already logged into;
• Continued packet theft – Finally, the attacker can simply continue stealing your data by sniffing your data packets.

How Do ARP Spoofing Attacks Work?

Now let’s take a look at how these attacks work step-by-step.

1. First, the hacker gains access to the LAN network and scans it for IP addresses;
2. Next, with an ARP spoofing tool, such as Arpspoof, the attacker creates ARP responses;
3. Then, the ARP packet with the hacker’s MAC address is sent and paired with the target’s IP address. This fools the router and the computer to connect to the hacker instead of to each other;
4. Now the ARP cache gets updated, meaning the router and the computer will communicate with the cybercriminal;
5. Other hosts on the network will then broadcast data to the attacker seeing the spoofed ARP cache.

Can You Detect ARP Spoofing?

The good news is that yes, you can detect an ARP spoofing attack.

There are several ways you can do this.

• Using Windows Command Prompt

If you are on Windows OS, you can find out if your computer attacked by ARP spoofing by typing

arp -1

In the command line.

What this will do is bring out an ARP table with the IP addresses on the left side and the MAC addresses in the middle. If two IP addresses share the same MAC address, this is a sign of an ARP attack.

Also, note that the same command for detecting ARP spoofing works with Linux as well.

• Using a 3rd-party software

If you are using 3rd-party software, there are two options available.

One is to use a dedicated ARP spoofing detection program such as XArp to monitor the network for ARP spoofing attacks.

The other is to use a network protocol analyzer like Wireshark.

How to Prevent ARP Spoofing (And Protect Your IP Address and MAC Address)?

Besides using an ARP spoofing detection software (or command), what else can you do to prevent such attacks?

There are several things you can do, such as:

1. Use packet filters to detect malicious data packets and block them;
2. Encrypt the data between you and the exit with a VPN (Virtual Private Network);
3. Use TLS (Transport Layer Security), SSH Secure Shell) and HTTPS to encrypt your data-in-transit and minimize the likelihood of ARP spoofing attacks;
4. Use static ARP to allow static entries for each IP address and prevent hackers to listen on ARP responses for that IP address;
5. Monitor address resolution using intrusion-detection software like Suricata;
6. Stay away from trust relationships that rely on IP addresses for authentication as they make it easier to conduct ARP spoofing attacks.

Conclusion

As you can see, ARP spoofing is definitely something to be wary of.

Hopefully, thanks to this article, you now have a better understanding of ARP spoofing attacks, how they work and how to detect and prevent them.