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What Is ARP Poisoning?

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ARP poisoning is a type of cyberattack that exploits weaknesses in the ARP protocol in order to disrupt, redirect, or spy on network traffic, allowing further attacks such as man-in-the-middle or DDoS attacks (Distributed Denial-of-Service attacks). In this blog post, we will explain what an ARP poisoning attack is, how it works, what are its main types, target systems, goal, and impact, as well as how you can help protect against it.

What is an ARP poisoning attack?

ARP poisoning is a type of attack in which an attacker sends fake Address Resolution Protocol (ARP) messages over a Local Area Network (LAN), this to associate the attacker’s Media Access Control (MAC) address with the IP address of a legitimate computer or server on the network.

An ARP poisoning attack can also be called ARP spoofing, ARP cache poisoning, ARP poison routing, or ARP MAC flooding. By intercepting all traffic destined for the target system, an attacker can read, modify, or delete that data, allowing for man-in-the-middle (MITM) or Denial-of-Service (DoS) attacks.

How does an ARP poisoning attack work?

An ARP poisoning attack occurs when an attacker crafts a forged ARP reply and sends it to the target system. The forged ARP reply contains the attacker’s MAC address and the IP address of the legitimate system or user that the attacker is trying to impersonate. When the target system receives this ARP reply, it updates its ARP table to associate the attacker’s MAC address with the IP address of the legitimate system. From this point on, all traffic destined for the legitimate system will be sent to the attacker instead.

What are the main types of ARP poisoning attacks?

An attacker can execute an ARP poisoning attack in either of the following two forms:

ARP spoofing

ARP spoofing is a type of attack where the attacker sends forged ARP replies to the target system. The attacker only needs to send one forged ARP reply for the target system to update its ARP table. ARP spoofing attacks are common because they are relatively easy to carry out.

ARP cache poisoning

ARP cache poisoning is a more sophisticated type of attack where the attacker sends multiple forged ARP replies to the target system. The attacker sends so many ARP replies that the target system’s ARP table becomes filled with invalid entries. As a result, the target system is unable to communicate with any other systems on the network.

What systems can be targeted by an ARP poisoning attack?

ARP poisoning attacks typically target systems acting as switches, gateways, or routers. This is because these types of systems typically have ARP tables that are large enough to store multiple entries. ARP poisoning attacks can also be targeted at individual systems, such as desktop computers or laptops.

What is the end goal of an ARP poisoning attack?

ARP poisoning attacks aim to intercept traffic destined for the target system. The attacker can then do the following:

Eavesdrop on the communication: The attacker can view or listen to the communication between two systems, such as email messages, instant messages, or VoIP conversations.

Modify the traffic: The attacker can modify the data being sent between two systems. For example, the attacker could change the content of an email message or redirect a web page to a different website.

Delete the traffic: The attacker can delete the data being sent between two systems, preventing it from reaching its destination.

Launch denial-of-service attacks: The attacker can launch denial-of-service attacks by flooding the target system with ARP replies. This will cause the target system to crash or become unresponsive.

What is the impact of an ARP poisoning attack?

The impact of an ARP poisoning attack can vary depending on the goals of the attacker. However, in general, ARP poisoning attacks can lead to the following impact or damage:

Data loss or theft

Data loss or theft means that the attacker can view, modify, or delete the data being sent between two systems. This can result in confidential information being leaked, such as trade secrets or customer data.

System downtime

System downtime means that the target system becomes unresponsive and is unable to process any traffic. This can cause disruptions to communications and lead to loss of productivity.

Reputational damage

ARP poisoning attacks can damage the reputation of an organization if sensitive information is intercepted and leaked. Sensitive information can be range from personal information to trade secrets.

How to protect against an ARP poisoning attack?

Several approaches can help protect your organization against ARP poisoning attacks:

Static ARP tables

You can statically map all MAC addresses in a network to their IP addresses within an ARP tables, although this approach can be time-consuming due to all the manual updates required.

Switch security

Dynamic ARP Inspection (DAI) can help to protect against ARP poisoning attacks. DAI works by comparing the ARP packets with the entries in the ARP table. If there is a mismatch, then the ARP packet is dropped and an alert is generated.

Virtual Private Networks (VPNs)

A VPN provides an extra layer of security as the data is encrypted before it is sent over the Internet, making a poisoning attack much more difficult to carry out.

Encryption

Encryption makes it difficult for the attacker to view or modify the data being sent between two systems, as the data is transformed into a ciphertext that can only be decrypted by the intended recipient.

Network segmentation

A well-segmented network allows you to isolate systems from each other, making it more difficult for an attacker to reach all the systems on a network. For example, you could segment a network into different subnets, each with its own ARP table.

Wrapping up

An ARP poisoning attack may seem at first glance like just another threat among all the other main cyber risks threatening organizations. But given its ability to lead to more sophisticated attacks, such as data theft, Man-in-the-Middle, or Denial-of-Service attacks, ARP poisoning should not be taken lightly. Your proactive approach could start with improving your network security through penetration testing, thus identifying vulnerabilities before attackers can exploit them.

An internal penetration test will help you determine if your network infrastructure is vulnerable to an ARP poisoning attack or other malicious attacks.

Contact us if you need help securing your networks with penetration testing.

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