ESXi ARP Spoofing Prevention

TL;DR

ARP spoofing attacks can disrupt network communication on your VMware ESXi host by associating the wrong MAC address with an IP address. This guide shows you how to harden your ESXi setup against these attacks using a combination of port security, static ARP entries and monitoring.

Steps to Prevent ARP Spoofing in ESXi

1. Understand the Risk
• ARP spoofing (also known as ARP poisoning) redirects network traffic by sending falsified Address Resolution Protocol (ARP) messages.
• On ESXi, this can lead to denial of service or man-in-the-middle attacks.
2. Enable Port Security on vSwitches

Port security limits the MAC addresses allowed to connect to a specific port group. This is your first line of defence.

1. Log in to the ESXi host via SSH or the web interface (vSphere Client).
2. Use the esxcli command to configure port security. First, find the vSwitch name:

   esxcli network vswitch standard list

3. Then, enable port security on the desired port group:

   esxcli network vswitch port security mac-learning disable --vswitch <vSwitch_Name> --portgroup <PortGroupName>

4. Add allowed MAC addresses. Replace XX:XX:XX:XX:XX:XX with the actual MAC address:

   esxcli network vswitch port security mac-address add --vswitch <vSwitch_Name> --portgroup <PortGroupName> --mac XX:XX:XX:XX:XX:XX

5. Verify the configuration:

   esxcli network vswitch port security mac-learning status --vswitch <vSwitch_Name> --portgroup <PortGroupName>

3. Implement Static ARP Entries

Static ARP entries manually map IP addresses to MAC addresses, preventing attackers from forging these associations. Use this for critical servers.

1. Identify the static IP and MAC address pairs you need to protect.
2. Add a static ARP entry using esxcli:

   esxcli network ip arp add --ip <IP_Address> --mac XX:XX:XX:XX:XX:XX

3. Verify the static ARP entry:

   esxcli network ip arp list

4. Monitor for ARP Anomalies

Regularly check your ESXi host’s logs and ARP tables for suspicious activity.

1. ARP Table Inspection: Use the command below to view the current ARP table. Look for unexpected MAC addresses associated with known IP addresses.

   esxcli network ip arp list

2. VMkernel Logs: Examine the VMkernel logs (accessible via vSphere Client or SSH) for ARP-related errors or warnings. Look for duplicate entries, which can indicate spoofing attempts.

   You may need to increase verbosity levels in the logging configuration to capture more detailed ARP information.

5. Consider Using a Network Intrusion Detection System (NIDS)

A NIDS can provide real-time monitoring and alerting for ARP spoofing attacks. Many commercial and open-source solutions are available.

6. Keep ESXi Updated

Regularly apply security patches and updates to your ESXi host to address known vulnerabilities that could be exploited by attackers.