“In a normal Layer-2 switch, the switch learns the MAC of the client by seeing it respond with its source address,” Moore explained. “This attack confuses the AP into thinking that the client reconnected elsewhere, allowing an attacker to redirect Layer-2 traffic. Unlike Ethernet switches, wireless APs can’t tie a physical port on the device to a single client; clients are mobile by design.”

The back-and-forth flipping of the MAC from the attacker to the target, and vice versa, can continue for as long as the attacker wants. With that, the bidirectional MitM has been achieved. Attackers can then perform a host of other attacks, both related to AirSnitch or ones such as the cache poisoning discussed earlier. Depending on the router the target is using, the attack can be performed even when the attacker and target are connected to separate SSIDs connected by the same AP. In some cases, Zhou said, the attacker can even be connected from the Internet.

“Even when the guest SSID has a different name and password, it may still share parts of the same internal network infrastructure as your main Wi-Fi,” the researcher explained. “In some setups, that shared infrastructure can allow unexpected connectivity between guest devices and trusted devices.”

No, enterprise defenses won’t protect you

Variations of the attack defeat the client isolation promised by makers of enterprise routers, which typically use credentials and a master encryption key that are unique to each client. One such attack works across multiple APs when they share a wired distribution system, as is common in enterprise and campus networks.

In their paper, AirSnitch: Demystifying and Breaking Client Isolation in Wi-Fi Networks, the researchers wrote:

Although port stealing was originally devised for hosts on the same switch, we show that attackers can hijack MAC-to-port mappings at a higher layer, i.e., at the level of the distribution switch—to intercept traffic to victims associated with different APs. This escalates the attack beyond its traditional limits, breaking the assumption that separate APs provide effective isolation.

This discovery exposes a blind spot in client isolation: even physically separated APs, broadcasting different SSIDs, offer ineffective isolation if connected to a common distribution system. By redirecting traffic at the distribution switch, attackers can intercept and manipulate victim traffic across AP boundaries, expanding the threat model for modern Wi-Fi networks.

The researchers demonstrated that their attacks can enable the breakage of RADIUS, a centralized authentication protocol for enhanced security in enterprise networks. “By spoofing a gateway MAC and connecting to an AP,” the researchers wrote, “an attacker can steal uplink RADIUS packets.” The attacker can go on to crack a message authenticator that’s used for integrity protection and, from there, learn a shared passphrase. “This allows the attacker to set up a rogue RADIUS server and associated rogue WPA2/3 access point, which allows any legitimate client to connect, thereby intercepting their traffic and credentials.”