Why open WiFi networks are a security risk

Open WiFi networks — the kind you find in hotels, cafes, and airports — are convenient. They're also surprisingly easy to exploit. Here's a real-world example of how MAC address spoofing can bypass access controls on an open network.

The scenario

While staying at a hotel, WiFi access was delayed due to a check-in process. The network was open (no WPA2 password), but access was restricted by MAC address — the router only allowed registered devices to connect.

The problem? On an open network, MAC addresses are trivially easy to spoof.

How MAC address spoofing works

Every network device has a MAC (Media Access Control) address — a unique identifier that routers use to recognize devices. On a secured network with WPA2 encryption, knowing a MAC address alone isn't enough. But on an open network, it's the only thing standing between you and internet access.

Using jamWifi, a macOS network scanning tool, we could see all devices currently connected to the hotel network along with their MAC addresses and packet activity.

After identifying a device with high traffic (indicating active use and a valid connection), we used a simple terminal command to change our device's MAC address to match theirs.

The result? Instant connection to the hotel WiFi.

The bigger picture

Once on the network, an attacker could potentially: - Perform man-in-the-middle (MITM) attacks to intercept unencrypted traffic - Sniff credentials sent over HTTP connections - Launch ARP spoofing attacks to redirect traffic through their device

How to protect yourself

• •Avoid open WiFi networks whenever possible. If you must use one, assume everything you do is visible.
• •Use a VPN to encrypt your traffic end-to-end, regardless of the network's security.
• •Stick to HTTPS — look for the padlock icon and avoid entering sensitive information on HTTP sites.
• •Forget the network after use so your device doesn't auto-connect later.

Open networks are convenient, but convenience and security rarely go hand in hand.