Sniffing Technique: ARP Poisoning

Sniffing Technique: ARP Poisoning

What is ARP Poisoning?

ARP (Address Resolution Protocol) poisoning, also known as ARP spoofing, is a type of cyber attack where an attacker sends falsified ARP messages over a local area network. This results in the linking of an attacker's MAC address with the IP address of a legitimate computer or server on the network.

Why is ARP Poisoning Important to Understand?

Understanding ARP poisoning is crucial for several reasons:

1. It's a common method used in Man-in-the-Middle (MITM) attacks
2. It can lead to data theft, session hijacking, and denial-of-service attacks
3. It exploits a fundamental protocol vulnerability rather than software flaws
4. It's relatively easy to execute but can have severe consequences
5. Knowledge of ARP poisoning is essential for network security professionals to implement proper defenses

How ARP Poisoning Works

1. Normal ARP Process: When a device wants to communicate with another device on the same network, it needs to know the MAC address corresponding to the target's IP address. It broadcasts an ARP request asking, "Who has this IP address?" The device with that IP responds with its MAC address.

2. The Attack: In ARP poisoning, the attacker sends false ARP messages to associate their MAC address with the IP address of another host (typically the default gateway). This causes traffic meant for that IP address to be sent to the attacker instead.

3. Result: The attacker can now intercept, modify, or simply monitor the traffic before passing it on to its intended destination (if they choose to forward it at all).

Technical Details:

- ARP has no authentication mechanism
- Most operating systems will update their ARP tables even if they didn't initiate an ARP request
- The attacker typically needs to send periodic spoofed ARP packets to maintain the poisoned state
- Tools like Arpspoof, Ettercap, and Wireshark are commonly used for ARP poisoning

Exam Tips: Answering Questions on ARP Poisoning

1. Understand the terminology: Know that ARP poisoning, ARP spoofing, and ARP cache poisoning refer to the same attack.

2. Know the prerequisites: Remember that ARP poisoning:
- Only works on local networks (same broadcast domain)
- Requires the attacker to have access to the local network
- Affects the data link layer (Layer 2) of the OSI model

3. Remember the detection methods:
- Static ARP entries
- ARP monitoring tools
- Packet analysis showing multiple devices claiming the same IP
- Unusual ARP traffic patterns

4. Know the mitigation techniques:
- Using static ARP tables when possible
- Implementing packet filtering
- Using VLANs to segment the network
- Deploying ARP spoofing detection tools
- Using encryption protocols (HTTPS, SSH, etc.)
- Implementing 802.1X port security

5. Common exam scenarios:
- Identifying ARP poisoning as the attack when symptoms include network traffic redirection
- Selecting the most effective countermeasure for a specific scenario
- Determining what information an attacker can gather through ARP poisoning
- Distinguishing ARP poisoning from other MITM attacks

6. Remember related attacks:
- DHCP spoofing
- DNS poisoning
- MAC flooding

7. Focus on the practical impact: Understand that ARP poisoning is primarily a means to an end (such as sniffing traffic, session hijacking, or denial of service) rather than an end itself.

When answering exam questions, always consider the context and scenario. Think about whether the network is vulnerable to ARP poisoning based on the description, and what the most effective countermeasure would be considering the constraints mentioned in the question.