Stop ARP Spoofing Attacks

TL;DR

ARP spoofing lets attackers intercept network traffic by linking their MAC address to your IP address. This guide shows you how to detect and prevent these attacks using static ARP entries, port security on switches, and monitoring tools.

What is ARP Spoofing?

Address Resolution Protocol (ARP) translates IP addresses into MAC addresses – essential for devices communicating on a local network. ARP spoofing tricks devices into associating the wrong MAC address with an IP address, allowing attackers to ‘listen in’ on your traffic or redirect it.

How to Detect ARP Spoofing

1. Check Your ARP Cache: Regularly inspect your ARP table for inconsistencies. On Windows:

   arp -a

   On Linux/macOS:

   arp -n

   Look for multiple MAC addresses associated with the same IP address – a strong sign of spoofing.

2. Use ARP Monitoring Tools: Several tools can detect ARP anomalies in real-time. Examples include:
   • Wireshark: A powerful network protocol analyser. Filter for ARP packets and look for suspicious entries.
   • Arpwatch: Monitors Ethernet networks for ARP changes and alerts you to potential spoofing.
   • XARP: Detects ARP reply collisions, indicating a possible attack.

How to Prevent ARP Spoofing

1. Static ARP Entries: Manually define the IP-to-MAC address mappings for critical devices. This prevents attackers from changing these entries.

   arp -s <IP Address> <MAC Address>

   For example:

   arp -s 192.168.1.1 AA:BB:CC:DD:EE:FF

   Important: Use this only for trusted devices as incorrect entries will break connectivity.

2. Port Security on Switches: Configure switches to limit the MAC addresses allowed on each port. This restricts attackers from connecting multiple devices to a single port and spoofing ARP requests.
   • Enable Port Security:

     switchport mode access

   • Limit MAC Addresses:

     switchport mac-address sticky

   • Shutdown Violations:

     switchport port-security violation shutdown

   Note: Switch configuration varies by manufacturer (Cisco, HP, etc.). Consult your switch documentation.

3. Use DHCP Snooping: If your network uses DHCP, enable DHCP snooping on switches. This prevents rogue DHCP servers from distributing incorrect IP addresses and ARP information.
   • Enable DHCP Snooping:

     ip dhcp snooping

   • Bind DHCP Snooping to Trusted Ports (ports connected to your legitimate DHCP server):

     ip dhcp snooping vlan <VLAN ID> trusted

4. 802.1X Authentication: Implement 802.1X port-based network access control for stronger authentication and authorization.
5. Regularly Update Firmware: Keep your network devices (switches, routers) updated with the latest security patches to address vulnerabilities.

Further Considerations

• ARP spoofing is typically a local network attack. Strong perimeter cyber security measures like firewalls won’t directly prevent it.
• Educate users about phishing attempts, as attackers often use social engineering to gain access to the network.
• Consider using tools that dynamically detect and block ARP spoofing attacks (e.g., some intrusion detection systems).