Free Internet? Unmasking Public Networks Hidden Flaw
How “pay-for-access” Wi‑Fi Networks Are Insecure – And What Can Be Done About It
Unauthorized access is illegal, and the techniques described here should not be used for any illicit purposes.
Introduction
Many street and apartment Wi‑Fi services(Majorly on many areas of Nairobi) work on a “pay-for-access” basis. For instance, a user might pay a small fee (for example, 30 KSH for 24 hours) to get online. In these setups, the network is often configured so that the password is embedded in the SSID and, after initial connection, users are redirected to a payment gateway. Once payment is completed, the network uses the device’s MAC address as an identifier to grant Internet access. While this may seem convenient, relying solely on the MAC address for authentication introduces a serious vulnerability.
The Vulnerability: MAC-Based Authentication
Wireless networks that use MAC addresses to assign access have a critical flaw:
- Broadcast in the Clear: MAC addresses are transmitted in clear text as part of the standard 802.11 protocol. This means that any device within range can capture these addresses using readily available packet‐sniffing tools.
- Ease of Spoofing: Most network interface controllers (NICs) allow the MAC address to be changed at the software level. Tools exist (for example, utilities like “macchanger”) that let a user modify the reported MAC address of their device.
- Implications: An attacker can simply capture the MAC addresses of devices that have paid for access and then modify (spoof) their own device’s MAC address to match one of these valid addresses. Once spoofed, the network—relying on that MAC as the sole identifier—will treat the attacker’s device as an authenticated user.
MAC addresses are inherently “public” on a wireless medium, using them for authentication creates a false sense of security.
How it’s done (For educational Purposes Only!)
The Hacker connects to the wifi (Most of the time the Wifi network is open or the password is on the SSID.
Upon connecting, the malicious user can view the other devices connected to the wifi together with their mac addresses.
The hacker notes the MAC Addresses of these devices.
Using macchanger (A linux Util). The hacker the spoofs their mac as of the victim thus maliciously getting internet access.
To prevent the victim from reconnecting(This may lead to packet loss) The hacker can use air-replay or ban it using bettercap’s arp.ban module.
Why This Matters
- Financial Loss and Service Abuse: When a hacker successfully spoofs a MAC address, they can gain free access to the service—defrauding the provider and possibly reducing network performance for paying customers.
- Privacy Risks: Not only can this enable unauthorized access, but it can also lead to further attacks (like man-in-the-middle scenarios) that jeopardize the privacy of other users on the network.
- False Security: Providers might believe that MAC filtering (or using MAC addresses to gate access) offers robust security, but in reality, it only deters very casual misuse and leaves the network vulnerable to even moderately skilled attackers.
Raising Awareness: Best Practices for Network Providers
While the technique of MAC spoofing is well known in the security community, the fact remains that many public and apartment Wi‑Fi setups still rely on this insecure method. Here are some recommendations for network operators to mitigate these vulnerabilities:
- Adopt Stronger Authentication Methods: Instead of using MAC addresses as the sole means of authentication, consider protocols like WPA2/WPA3 Enterprise that integrate additional forms of identity verification (e.g., RADIUS with certificate-based authentication).
- Encrypt All Traffic: Implement end-to-end encryption so that even if an attacker gains access, the data they intercept is protected.
- Segment the Network: Use VLANs or guest networks to isolate users and limit the potential damage from unauthorized access. Most of these networks are not properly segmented which poses a security risk since devices can reach up to 50.
- Educate Users: Inform customers about the risks of open or loosely secured networks and encourage best practices for protecting their own devices.
Conclusion
The reliance on MAC addresses for authentication in pay-per-use Wi‑Fi systems creates an easily exploitable vulnerability. Even though many in the security community have demonstrated methods (such as using packet sniffing tools and MAC spoofing utilities) to bypass these controls, the goal here is to raise awareness. By understanding these risks, network providers can take meaningful steps to secure their systems and protect both their revenue and the privacy of their users.
Disclaimer: The information presented in this article is provided for educational and awareness purposes only. It is not intended to encourage or instruct on illegal activities. Unauthorized access to networks is a criminal offense in many jurisdictions.
