What is ARP Poisoning? 

ARP (Address Resolution Protocol) Poisoning, also called ARP SpoofingWhat is Spoofing? Spoofing is an attack method whereby bad actors masquerade as someone or something else to win a victim’s trust. Their motivation is to gain access to systems,… More, is a type of attack where a bad actor sends modified frames over a local network. This manipulates the ARP cache of network devices, allowing the actor to associate their Media Access Control (MAC) address with the IP address of another device, such as a legitimate server or router. 

Once successful, the malefactor can intercept, modify, or even stop network traffic, leading to serious security risks like data theft, session hijacking, or Man-in-the-MiddleWhat is a Man-in-the-Middle Attack? A Man-in-the-Middle (MitM) cyberattack is a threat where an attacker secretly intercepts and possibly alters the communication between two parties who believe they are directly… More (MitM) attacks. 

How Does ARP Poisoning Work? 

ARP is a protocol used in IPv4 networks to discover MAC addresses of other hosts. Since ARP operates at Layer 2 of the OSI model, it does not have built-in authenticationWhat is Authentication? Authentication is the process by which the identity of a user or system is verified. It ensures that the entity attempting to access a resource is who… More mechanisms, making it susceptible to spoofing attacks. ARP Poisoning works in the following steps: 

 Scanning the Network: The threat actor first scans the local network to identify active devices and their corresponding MAC addresses. 

1. Spoofing ARP Responses: The attacker sends malicious ARP replies, falsely linking their MAC address to a legitimate IP address (a gateway or server). 
2. Intercepting Network Traffic: Once devices update their ARP caches with the spoofed entry, all traffic intended for the legitimate IP address is routed to the attacker’s device. 
3. Manipulating or Relaying Data: The attacker can eavesdrop, alter data packets, or perform a Denial-of-Service (DoS) attack by dropping packets entirely. 

Common Uses of ARP Poisoning 

ARP Poisoning is often used as a stepping stone for more advanced cyberattacks, including: 

Man-in-the-Middle (MitM) Attacks: The bad actor secretly intercepts and alters communications between two parties without them knowing. 

• Session Hijacking: By capturing session cookies, a criminal can take over a user’s authenticated session and get access to sensitive systems. 

• Denial of Service (DoS): Flooding the network with fake ARP responses can cause network instability, resulting in service disruptions. 

• Credential TheftWhat is Credential Theft? Credential theft is a type of cyberattack in which attackers steal a victim’s login details, such as usernames, passwords, or other forms of authentication. This stolen… More: Intercepted login credentials from unencrypted connections can be used to gain unsanctioned access to accounts. 

Detecting ARP Poisoning 

Since ARP does not inherently verify the authenticity of address mappings, ARP Poisoning can be difficult to detect. However, there are several techniques security teams can use to identify potential ARP-based attacks: 

Network Monitoring: Analyzing ARP tables and traffic patterns for inconsistencies, such as multiple MAC addresses mapping to the same IP address. 

• Packet Inspection Tools: Network packet analyzers like Wireshark can capture and analyze ARP traffic to detect irregularities. 

• Static ARP Entries: Configuring static ARP entries for critical devices prevents them from being altered dynamically by an attacker. 

• IDS/IPS Solutions: Intrusion Detection and Prevention Systems (IDS/IPS) can detect and block suspicious ARP activity. 

Preventing ARP Poisoning 

Entities can implement several security measures to mitigate the risks associated with ARP Poisoning: 

Enable Dynamic ARP Inspection (DAI): DAI validates ARP information against a trusted database, preventing spoofed responses. 

• Use ARP Spoofing Detection Tools: ARP spoofing detection tools like ARPwatch and XArp help monitor and alert administrators about ARP anomalies. 

• Encrypt Network Traffic: Using secure protocols such as HTTPS, SSH, and VPNs ensures that intercepted data remains unreadable. 

• Implement VLAN Segmentation: VLANs malefactors’s ability to move laterally across a network, limiting exposure to ARP Poisoning. 

• Regularly Audit ARP Tables: Periodic review of ARP entries on critical network devices helps detect unauthorized changes. 

 ARP Poisoning is a concerning threat in local networks due to the inherent weaknesses in the ARP protocol. Cybercriminals use this technique to intercept, manipulate, and disrupt network communications, leading to data breaches and security incidents. 

 However, firms can mitigate these risks by implementing proactive security measures, such as network monitoring, encryptionWhat is Encryption? Encryption converts readable data (plaintext) into a scrambled and unreadable format (ciphertext) using an algorithm and a key. The primary purpose of encryption is to ensure the… More, and ARP inspection tools. Bolstering defenses against ARP Poisoning is key to maintaining a secure and resilient network infrastructure. 

 For more essential cybersecurity definitions, visit our glossary pages here.