What Is ARP Spoofing, and Why Should You Care?

Imagine an attacker infiltrating an enterprise LAN and redirecting all traffic meant for the company’s gateway to their own device. That’s what ARP spoofing is. To understand this attack, we’ll start with the foundation: the ARP protocol. 

What is the purpose of the ARP protocol? 

Imagine trying to send a letter to a friend. You know their name but not their address. This is the challenge computers face daily and why the ARP protocol is so important. 

Let’s say your computer wants to communicate with another device on your network, such as a printer. To do this, it needs two addresses: the printer’s IP address and its corresponding MAC (media access control) address. 

Now, your computer likely already knows the printer’s IP address (typically assigned by DHCP) but it doesn’t have the MAC address. 

This is where ARP (Address Resolution Protocol) comes in. It maps the printer’s IP address to the right MAC address. 

To communicate with the printer, your computer first checks its ARP cache, a temporary table that contains IP-to-MAC mappings. If the mapping exists or the MAC address of the destination IP is in the cache, your computer will use it to start communications with the printer. 

If the mapping doesn’t exist, your computer will send an ARP request broadcast to every device in your network and ask, "Who has this IP address?” 

The device with that IP will then reply with its MAC address, ensuring that data flows seamlessly to the right party. 

But what happens when a malicious actor exploits this process? That’s what ARP spoofing is, when attackers send fraudulent ARP responses to trick your device into sending data to the wrong place. 

Ultimately, ARP’s weakness lies in its stateless attribute, which accepts ARP replies even when no ARP queries have been sent out. 

Below, we explore what ARP spoofing is and how you can protect your network. 

What is ARP spoofing? 

ARP spoofing is a type of cyber-attack that allows attackers to intercept communications between two devices in a network. 

Here's how it works: 

• First, the attacker scans your local network to identify active devices and their IP addresses. This helps them understand your network layout and select valuable targets like routers, Active Directory servers, or email servers. 

• Next, the attacker broadcasts a forged response across the network, linking their MAC address to the IP address of say, your email server.  

• In response, multiple devices in your network update their ARP cache to link the attacker’s MAC address to your email server’s IP address.  

• Once this happens, all communications between your device and the email server are redirected to the attacker’s machine. This allows the attacker to intercept, modify, or even block communications altogether. 

• Optionally, the attacker may even forward the intercepted traffic to your device, so you aren’t the wiser that your communications have been compromised. 

This leads us to two interesting questions we’re often asked. 

What’s the difference between ARP cache spoofing and ARP poisoning? 

As can be seen, ARP spoofing is when an attacker links their MAC address to a legitimate IP address. 

Meanwhile, ARP poisoning is the result of ARP spoofing. 

Attack technique: ARP spoofing	When an attacker sends fraudulent ARP messages to the entire network
The resultant damage: ARP poisoning	The corruption of device ARP caches with incorrect IP-to-MAC mappings

The terms are often used interchangeably, but it’s worth noting that ARP spoofing is the method of attack, while ARP poisoning is the outcome of the attack. 

What’s the difference between ARP spoofing and DNS spoofing?  

In ARP spoofing, attackers target a local network by manipulating ARP caches to redirect traffic to their machine. 

Meanwhile, DNS poisoning targets the DNS resolution process (which is how domain names are translated into IP addresses). 

The attacker corrupts DNS caches to redirect users to malicious IP addresses, even though they may have entered a legitimate domain name. 

Why is ARP spoofing dangerous? 

Far from being harmless, ARP spoofing is a favorite tool of cybercriminals such as: 

• Transnational crime syndicates. These attackers are primarily motivated by financial gain. They use ARP spoofing to intercept sensitive information like login credentials, credit card numbers, and corporate data. Once they have this information, they use it to commit financial fraud, deploy ransomware, replicate innovations, or sell proprietary designs to competitors. 

• Hacktivists. Motivated by political or ideological causes, hacktivists use ARP spoofing to disrupt services, spread their message, or expose what they believe is wrongdoing by organizations and governments. By intercepting and leaking sensitive communications, they hope to cause reputational harm to their targets or draw public attention to their causes. 

• Nation-state actors. These sophisticated attackers often have extensive resources and primarily use ARP spoofing for espionage or intelligence gathering. Their main targets are governmental or corporate networks.  

ARP spoofing attacks are often the launching pad for DDoS, session hijacking, and MiTM (main-in-the-middle) attacks. 

Can ARP spoofing be detected? 

The short answer is yes. 

Knowing how to detect ARP spoofing is critical, and here’s how you can do it. 

• For your local network, do a manual check using the built-in functionality of your OS. In the command line (whether Windows or Linux), type arp –a to check your ARP cache. This command displays the list of IP addresses and their associated physical MAC addresses on your network. If you see the same MAC address listed for multiple IP addresses, that’s a red flag. 

• If you have a larger network, consider specialized ARP spoofing detection tools like Wireshark or XArp. These programs continuously monitor network traffic, saving you from manual checks. XArp, for instance, watches for sudden spikes in gratuitous ARP messages (unsolicited ARP replies announcing IP-to-MAC mappings), which can indicate an attack. This proactive tool sends alerts when these spikes occur. 

• You can also leverage real-time data analysis of ARP traffic and machine learning algorithms to detect spoofing attempts. In 2024, researchers tested several machine learning algorithms such as Random Forest, Long Short-Term Memory (LSTM) Networks, Convolutional Neural Networks (CNNs), Support Vector Machines (SVM), and Isolation Forest. 

Random Forest showed the highest accuracy (around 94%) in identifying actual positives and filtering out false negatives. The advantage of machine learning is the capacity to learn from past attack patterns and adapt to new ones, enabling faster and more accurate ARP spoofing detection. 

Stronger together: The dual defense of network controls and credential security 

How to prevent ARP spoofing with network security best practices 

As mentioned, ARP spoofing exploits the ARP protocol’s trust model. However, these network controls form a formidable defense, protecting the integrity and confidentiality of network communications. 

Prevention method	What it does	Why it helps
Static ARP entries	Manually sets fixed IP-to-MAC address pairings on critical devices like routers and switches	Blocks devices from accepting unauthorized or spoofed ARP replies
Packet filtering	Allows network devices to filter and block suspicious ARP packets from unauthorized devices	Stops fraudulent ARP traffic before it reaches devices
Virtual Private Networks (VPN)	Encrypts all network traffic through a secure tunnel	Protects data even if intercepted, making it unreadable
Dynamic ARP inspection (DAI)	A security features that validates ARP packets in a network	Allows switches to intercept, log, and discard ARP packets with invalid IP-to-MAC address bindings
Encrypted protocols	Protects against data compromise with HTTPS, SSH, or TLS	Prevents attackers from intercepting sensitive communications
Zero trust network segmentation	Isolates sensitive devices in separate network zones	Limits attack scope and lateral movement
802.1x port authentication	Ensures devices must authenticate (with RADIUS) before sending traffic	Reduces the risk of rogue devices injecting malicious ARP packets. Best used in tandem with DAI
Certificate pinning	Ensures apps are hardcoded to trust only specific certificate hashes	Without a valid certificate, attackers can’t “read” the traffic even if they intercept it   Note:   *Ensure pinned certificates can be updated on short notice   **Some industry regulations require rotation or revocation of certificates in as little as 24 hours for certain situations
IPv6 with SEND (Secure Neighbor Discovery)	SEND uses Cryptographically Generated Addresses (CGA) and digital signatures	Eliminates ARP entirely, replacing it with a protocol that’s resistant to ARP spoofing.   Note:   *SEND only works in IPv6, not IPv4 networks.

How to get seamless credential security with LastPass

If attackers somehow manage to bypass the above network controls, LastPass can be a strong ally in credential security. Here’s how: 

Military-grade AES encryption

With LastPass, your sensitive information is protected with AES-256 encryption. So, even if an attacker intercepts your data, this quantum-resistant encryption keeps your data hidden and indecipherable.  

URL encryption

With URL encryption, every URL is stored in an encrypted state. Even if attackers break in, they’ll still need to crack the ciphertext to identify the login credentials associated with each URL. This means your accounts stay safe from unauthorized access.  

Phishing resistant FIDO2 MFA

FIDO2 MFA adds an ironclad second form of authentication with either a hardware security key or passkeys. Because this type of MFA requires either a physical key or biometric authentication, stolen credentials alone won’t unlock your accounts. 

Transparent compliance

At LastPass, we operate with full transparency and adhere to the strictest data privacy standards such as GDPR and CCPA. And that’s not all: Our battle-tested infrastructure is regularly audited by world-class security organizations, and our new Compliance Center gives you 100% visibility into our latest certifications and security documentation. 

This means you can trust that your info is managed responsibly, and your privacy is our #1 priority. 

Continuous Dark Web Monitoring

If cybercriminals successfully use ARP spoofing to intercept your data, chances are your credentials may end up for sale on the Dark Web. 

LastPass Dark Web Monitoring monitors your email addresses continuously. This means you’ll know the moment your data is compromised, so you can change your passwords before damage happens. 

What I like best about LastPass is how easy it is to use and the number of features it includes. I was super easy to implement in our company. We use LastPass daily and we appreciate the great customer support (Stacey M, IT System Administrator and verified G2 reviewer).

If you’re ready to enjoy greater peace of mind and effortless security, unlock your LastPass free trial today (no credit card required). 

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