Control File Sharing with Mac Addresses

G5 Cyber Security

1 month ago

TL;DR

Yes, you can control access to file shares on a network using MAC addresses, but it’s not foolproof. This guide explains how to set this up on common operating systems and the limitations involved.

How to Control File Sharing with Mac Addresses

Understand MAC Addresses

A MAC address is a unique identifier assigned to a network interface card (NIC). It’s like a hardware serial number.
You’ll need the MAC addresses of all devices you want to allow or block access to your file share. You can find this in your device’s network settings. On Windows, use ipconfig /all in Command Prompt; on macOS, use System Preferences > Network > Advanced > Hardware.

Windows File Sharing (using the Hosts file)

Windows doesn’t have a built-in MAC address filter for shares directly. The most common workaround is using the hosts file, but this only blocks access based on IP addresses, which can change if DHCP is used. However, you can combine it with static IPs.

Assign Static IPs: First, assign a static IP address to each device you want to control. This prevents their IP from changing.
Edit the Hosts File: Open C:WindowsSystem32driversetchosts as an administrator in Notepad.
Block Access: Add lines like this for devices you want to block (replace with actual IPs):
```
127.0.0.1   192.168.1.10  # Block device with IP 192.168.1.10
```
Save the File: Save the changes to the hosts file. You may need administrator privileges.

macOS File Sharing (using `pf` firewall)

macOS offers a more robust solution using its built-in packet filter (`pf`) firewall.

Enable Packet Filter: Open Terminal and run sudo pfctl -e to enable the packet filter. You’ll be prompted for your password.
Create a Configuration File: Create or edit `/etc/pf.conf` using a text editor (like `nano` or `vim`). You’ll need administrator privileges.
```
sudo nano /etc/pf.conf
```
Add Rules: Add rules to allow or block MAC addresses. Example:
```
block return on en0 proto tcp from {MAC_ADDRESS} to any port {PORT}
pass in on en0 proto tcp from {MAC_ADDRESS} to any port {PORT} keep state
```
Replace en0 with your network interface (check System Preferences > Network), {MAC_ADDRESS} with the MAC address you want to allow/block, and {PORT} with the file sharing port (usually 548 for AFP or 139/445 for SMB).
Load the Configuration: Run sudo pfctl -f /etc/pf.conf to load the new rules.
```
sudo pfctl -f /etc/pf.conf
```
Check Status: Run sudo pfctl -s info to verify that the firewall is active and your rules are loaded.

Network Routers (Recommended)

The most effective way to control file sharing by MAC address is through your network router’s settings.

Access Router Settings: Log in to your router’s web interface (usually via a browser, using an IP like 192.168.1.1 or 192.168.0.1).
MAC Address Filtering: Look for MAC address filtering options. These are usually found in the Wireless Security or Access Control sections. The exact location varies by router manufacturer.
Allow/Block Devices: Add the MAC addresses of devices you want to allow or block access to your network (and therefore, file shares).
Save Changes: Save the changes and reboot your router if necessary.

Limitations & Considerations

MAC Address Spoofing: MAC addresses can be spoofed (changed by a user). This means someone technically skilled could bypass these restrictions.
DHCP: If devices use DHCP, their IP address may change, rendering the hosts file method ineffective unless combined with static IPs.
Network Complexity: Managing MAC addresses can become complex on larger networks.
Security Focus: MAC address filtering is a basic security measure and shouldn’t be relied upon as your only form of cyber security protection. Use strong passwords, encryption, and other security best practices.