ARP spoofing, also known as ARP poisoning, ARP cache poisoning, or address resolution protocol spoofing, is a type of attack that targets local area networks by exploiting a basic design flaw in the ARP protocol: trust.
A malicious actor sends forged ARP messages that falsely link their own MAC address - the unique hardware identifier assigned to a network interface - to the IP address of another device on the network, often a gateway or a server. Once this false mapping is accepted, traffic meant for the legitimate device is rerouted to the attacker. They can intercept data, manipulate it, or drop it altogether. In effect, the attacker impersonates a trusted machine. Because ARP doesn’t verify senders, the rest of the network simply accepts the update.
The ARP tables or caches on the victim devices now hold these fake MAC-IP associations. This corrupted state is known as ARP poisoning. While "ARP spoofing" refers to the act of sending forged messages, "ARP poisoning" describes the outcome. The terms are often used interchangeably, the distinction becoming useful when breaking down how the attack works.
ARP spoofing often serves as a stepping stone to more serious compromises, such as man-in-the-middle attacks, session hijacking, or silent data theft. It thrives in network environments that rely on implicit trust, which is still the default in most local area networks.
The Address Resolution Protocol, or ARP, lets devices on a local IPv4 network discover each other. In IPv6 networks, this role is taken over by the Neighbor Discovery Protocol, or NDP. ARP maps IP addresses - used by software - to MAC addresses, which are needed for actual data transmission on the network. It sits between the network and data link layers, quietly resolving the details that make communication possible.
When a device wants to send data to another on the same LAN, it first checks its ARP cache, also known as the ARP table. This is a local store of recently resolved IP-to-MAC mappings. If there’s no entry, it broadcasts a request across the network asking which device owns a particular IP address. The device with the matching IP replies with its MAC address. That information gets stored in the cache to avoid repeating the process every time.
The protocol works quickly and with minimal overhead, but there’s a catch. ARP was designed for simplicity, not security. It doesn’t verify the sender or check whether the information is legitimate. Devices accept and store ARP replies, even if they didn’t ask for them. These unsolicited messages, often called gratuitous ARP, are treated the same as replies to actual requests. If the cache already contains a mapping for that IP address, it gets replaced - no questions asked, whether the previous entry was expired or still valid.
This stateless and trust-based design makes ARP efficient, but also vulnerable. There’s no built-in safeguard to confirm that a message is genuine. As a result, any device on the network can inject false information, and the rest will accept it. This foundational weakness is what makes ARP spoofing not just possible, but effective.
At the core of an ARP spoofing attack is a simple manipulation of network trust. The attacker sends forged ARP messages, convincing devices on a local network to link the attacker’s MAC address with the IP of a legitimate host, usually the default gateway or a specific high-value device. Once accepted, this false mapping reroutes traffic through the attacker’s machine.
'The process starts with scanning. The attacker maps out active devices and their IP-MAC pairs using tools like nmap or arp-scan. From there, they craft fake ARP replies that say, in effect, “this IP is mine.” These messages are sent to both the target device and the gateway. That dual poisoning ensures that traffic flows through the attacker in both directions.
To avoid interrupting communication and tipping off users, attackers typically enable IP forwarding. This allows intercepted traffic to continue moving toward its intended destination.
Maintaining that position takes repetition. ARP cache entries are temporary. Attackers keep sending forged replies at intervals to prevent the real information from returning. ARP doesn’t verify updates; it simply accepts the most recent one, even if the previous entry is still valid.
Man-in-the-Middle (MitM): Bidirectional poisoning allows the attacker to intercept traffic, alter it, or observe silently.
Session Hijacking: Once in the traffic stream, the attacker can lift session tokens or cookies - those little bits of data that prove who you are. With the right one, they don't need a password. They're already inside.
DNS Spoofing via ARP: With a MitM position established, attackers can inject fake DNS replies and steer users to malicious websites.
Data Interception: Sometimes the goal isn’t disruption or modification. The attacker simply listens, collecting credentials or sensitive data.
These tools were originally developed for legitimate use in network diagnostics, penetration testing, or cybersecurity research. When used ethically and legally - within environments where permission has been granted - they help professionals identify and fix vulnerabilities. Like many powerful tools, they can be misused, but that misuse falls outside their intended design and lawful application.
Arpspoof - A lightweight command-line tool from the Dsniff suite. It's often used in lab setups to simulate what happens when ARP messages get forged - not for causing harm, but for understanding how networks react under stress.
Ettercap - A flexible, hands-on tool for inspecting traffic between devices on a LAN. It's a favorite among security testers when they need to dig into protocol behavior or simulate man-in-the-middle conditions safely.
Cain & Abel – A legacy Windows tool with features for password recovery and network diagnostics, including ARP spoofing simulations.
BetterCAP – A modern, modular framework for observing and manipulating traffic in test scenarios, particularly useful in lab environments.
MITMf – Built for security testing involving man-in-the-middle conditions, supporting a variety of testing modules.
Wireshark – A network protocol analyzer widely used for monitoring, debugging, and verifying network activity. Often paired with controlled ARP spoofing tests to visualize packet flow.
ARP spoofing changes how devices see each other. Once an attacker controls those mappings, they can intercept or redirect traffic with minimal effort.
In unencrypted protocols, intercepted data is exposed. With encrypted traffic, attackers can still observe metadata: connection patterns, endpoints, timing. That alone can be useful. In some cases, session tokens can be extracted and reused to impersonate users, bypassing login steps entirely. It’s a straightforward way to set up a man-in-the-middle position. From there, traffic can be monitored passively or altered. That might mean redirecting DNS queries, tampering with downloads, or injecting payloads into what appears to be legitimate traffic.
Spoofing can also introduce instability. Redirecting traffic to non-existent devices, flooding caches with fake entries, or overwhelming interfaces may disrupt services like DHCP, internal DNS, or authentication. The effects aren’t always immediate, but they often show up as slowdowns, dropped sessions, or support tickets without an obvious root cause. A broader issue is that many network controls - VLANs, ACLs, firewalls - assume the ARP layer is reliable. When that assumption breaks, controls higher in the stack may not behave as expected. An attacker who compromises one device can sometimes move laterally across a segment that should have been isolated.
When spoofing exposes sensitive or protected data, it usually triggers legal and regulatory consequences. Regulations like GDPR, HIPAA, or CCPA don’t differentiate based on technique. If data is intercepted or redirected, organizations may be required to disclose the incident and respond to follow-up scrutiny.
There are real-world campaigns where ARP spoofing was part of the attacker’s toolkit. In one case, attackers used it to inject HTML into live sessions, redirecting users to malicious content. In another, it gave them access to Remote Desktop and SMB traffic, including credentials. Both examples involved persistent, targeted activity, not opportunistic hits. These kinds of incidents are especially problematic in regulated environments. When spoofing provides a foothold into systems handling financial records, health data, or internal communications, the issue isn’t just technical. It can trigger mandatory reporting, audits, or legal action.
Start with the ARP cache. Commands like arp -a or ip neigh show let you inspect the mappings. If multiple IPs point to the same MAC address, or a familiar IP suddenly maps to something unfamiliar, that’s worth attention. The same goes for default gateway entries that shift without cause.
Some signals aren’t in the cache. Gratuitous ARP replies - devices announcing their MAC-IP mapping without being asked - can flood the network during an attack. A burst of them from a single source is a useful indicator. Repeated incomplete ARP entries can point to probing or interference, especially when clustered.
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Common Indicators and How to Spot Them |
What It Suggests |
How to Detect |
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Duplicate MAC entries |
Same MAC linked to multiple IPs, or vice versa |
Inspect with arp -a or ip neigh show |
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Gateway MAC changes |
A trusted IP is suddenly tied to a different MAC |
Compare ARP entries against expected values |
|
Gratuitous ARP replies |
Unsolicited broadcasts used to poison caches |
Capture with Wireshark using arp.duplicate-address-detected |
|
Incomplete ARP entries |
Potential probing or failed resolution attempts |
Look for patterns in ARP tables over time |
|
Unfamiliar MACs on known IPs |
Likely spoofed associations |
Cross-check against DHCP leases or static records |
For more active monitoring, tools like Wireshark, XArp, and ARPWatch are reliable choices. Wireshark filters can isolate unusual ARP traffic; XArp tracks both passive anomalies and probes actively; ARPWatch logs changes and alerts on shifts in MAC-IP pairings. On smaller networks, even a script that checks cache entries on critical machines can go a long way.
On the infrastructure side, managed switches may flag when the same MAC appears across ports. IDS systems like Snort or Suricata can detect known ARP spoofing patterns. A well-tuned SIEM can help connect events that seem unrelated on their own - log anomalies from a firewall, odd ARP traffic on a host, a port alert from a switch.
RASP (Runtime Application Self-Protection) isn’t designed to detect ARP spoofing, but it might catch what happens next: session changes, invalid certificates, or rerouted connections. It’s not the first place to look, but in high-sensitivity environments, it can add another signal.
No single method covers everything. Manual checks surface anomalies at the endpoint. Network-wide tools catch broader patterns. The goal is overlap so you have enough coverage to spot what shouldn't be there.
ARP spoofing works because devices accept whatever mapping they’re told. Prevention is about reintroducing skepticism through controls, validation, and awareness.
Static ARP entries provide fixed mappings between IP and MAC addresses. This can lock down communication paths for critical devices like gateways or DNS servers. It’s useful in small or stable segments, but doesn’t scale well across dynamic or user-facing environments.
Dynamic ARP Inspection (DAI) catches spoofed packets at the switch level. It validates ARP replies against a known-good list, usually one built by DHCP snooping. If the mapping doesn’t match, the packet is dropped. To work properly, DHCP snooping has to be enabled first. IP Source Guard builds on this by blocking traffic that doesn’t match expected IP-MAC-port bindings.
Port security adds a layer of restriction by limiting how many MAC addresses can be learned on each switch port, which can prevent spoofing attempts through physical access points.
Encryption won’t block spoofing, but it changes the stakes. VPNs, HTTPS, and SSH don’t stop redirection, but they prevent attackers from seeing or modifying the contents of what they intercept. That’s often enough to make spoofing unproductive.
Network segmentation limits the damage. By isolating sensitive systems into VLANs or separate trust zones, any successful spoofing attack is boxed into a smaller footprint.
Monitoring tools that flag unexpected ARP entries or broadcast storms are essential in catching what slips through. At a minimum, teams should be able to audit changes to ARP mappings and receive alerts for suspicious activity.
User awareness and patching also matter. Users trained to avoid untrusted networks or recognize hijacked sessions are less likely to fall into downstream traps. Keeping devices and firmware updated helps close the gaps that attackers try to exploit once they’re in.
Host-level tools like ArpON or ARPDefender validate ARP traffic locally. Some rely on predefined rules; others use dynamic learning or cryptographic techniques. GUI-based tools like XArp are useful for smaller setups or environments where admins need quick visual feedback.
Network-level protections like DHCP snooping, DAI, IP Source Guard, and port security are supported by most enterprise switches. These features create a verification layer for traffic at ingress points.
NAC systems (e.g., 802.1X) enforce device identity before granting network access, reducing the chances that unauthorized hardware can even start spoofing.
None of these tools are silver bullets, but together they make ARP spoofing harder to attempt and easier to contain.
ARP spoofing doesn’t happen in isolation, it’s often the first move in a longer sequence of lateral movement, credential theft, or session hijacking. Bitdefender’s GravityZone platform is built to address that full lifecycle: identifying threats early, disrupting them midstream, and closing the gaps that let them in.
Before an attack, GravityZone’s Risk Management and Patch Management capabilities help organizations reduce exposure by identifying configuration weaknesses and ensuring systems stay updated - critical when attackers scan for systems that will quietly accept poisoned ARP entries.
GravityZone External Attack Surface Management (EASM) can help organizations identify external-facing assets. While not a direct preventative measure, EASM can play an indirect but important role by reducing the overall attack surface and identifying vulnerabilities that an attacker might use to gain access to your internal network in the first place, which is a prerequisite for launching an ARP spoofing attack.
During the attack, Network Attack Defense can detect traffic anomalies typical of ARP spoofing and subsequent activity like credential theft or rogue routing. At the same time, tools like Anomaly Detection, which detects behavioral deviations in user and system activity, and Extended Detection and Response (XDR), which correlates events across the network and endpoints, help identify signs of compromised communications early.
For attacks that evade early controls, Managed Detection and Response (MDR) brings continuous oversight and expert-driven response. And in environments where tampering occurs (whether to registry settings, routing tables, or ARP caches), system-wide Integrity Monitoring offers critical visibility and rollback capability.
For long-term hardening, tools like PHASR (Proactive Hardening and Attack Surface Reduction) adapt endpoint behavior to reduce unnecessary exposure, while Offensive Security Services simulate real-world ARP-based attacks, helping teams test defenses before it counts.
Whether ARP spoofing is the entry point or a step in a more complex breach, GravityZone gives defenders the visibility, automation, and expertise to respond decisively without relying on luck or Layer 3 assumptions.
Yes. ARP spoofing operates at the data link layer (Layer 2) of the OSI model, while most firewalls inspect traffic at the network or transport layers (Layers 3 and 4). Because firewalls evaluate IP-based rules, they are generally blind to ARP activity, which manipulates MAC-to-IP address mappings inside a local network.
This mismatch allows an attacker to send falsified ARP replies and reroute traffic before it ever reaches the firewall, effectively sidestepping traditional inspection points. Even advanced packet filtering or segmentation rules won’t apply once the traffic is misdirected at Layer 2.
Some next-generation firewalls or security appliances may include ARP-aware detection modules or integrate with switch-level protections like Dynamic ARP Inspection (DAI). However, for most enterprise networks, ARP spoofing represents a foundational blind spot that must be addressed at the infrastructure level - through switch configurations, monitoring tools, and proactive MAC-IP validation mechanisms.
None - ARP doesn’t show up in IPv6. Its job in IPv4, mapping IP addresses to MAC addresses, is handled in IPv6 by something else: the Neighbor Discovery Protocol, or NDP.
NDP isn’t just a rename. It works differently, using multicast instead of broadcast, and comes with optional security features like Secure Neighbor Discovery (SEND), which adds cryptographic validation to prevent spoofing. That said, those features aren’t always implemented in practice, and NDP itself can be a target if left unprotected.
For organizations moving toward or already using IPv6, the takeaway is this: ARP spoofing doesn’t apply, but that doesn’t mean address resolution is off the table from a security perspective. The model changes. The risks shift. And new configurations come into play. It’s not a free pass - it’s just a different protocol with its own set of expectations.
ARP spoofing and IP spoofing are both deception techniques, but they occur at different OSI layers and serve different attack purposes.
ARP spoofing takes place at Layer 2 (Data Link Layer) within a local area network. An attacker sends forged ARP replies to associate their MAC address with the IP of a trusted host, typically to intercept, alter, or drop traffic between endpoints. It’s confined to the broadcast domain and is a common enabler of man-in-the-middle (MitM) attacks.
IP spoofing, by contrast, operates at Layer 3 (Network Layer) and involves sending packets with a falsified source IP address. This is often used to bypass IP-based access controls, hide an attacker’s identity, or conduct external attacks such as SYN floods in denial-of-service campaigns.
In short, ARP spoofing targets local traffic routing by corrupting device caches, while IP spoofing manipulates headers to deceive remote systems or mask origin. Both require different detection strategies and affect different parts of the network stack.