Mathy Vanhoef and Frank Piessens, KU Leuven, Belgium

The 4-way Wi-Fi handshake is used to negotiate fresh pairwise keys, and authenticates both the client and Access Point (AP). We analyze this handshake, and discover several new denial-ofservice (DoS) attacks against it. Interestingly, our attacks work even if Management Frame Protection (MFP) is enabled. The first attack abuses the observation that messages in the 4-way handshake undergo linklayer encryption once the pairwise key is installed. More precisely, when message 4 of the handshake is dropped, the handshake times out. The second attack is similar to the second one, but induces the AP into sending the first message 4 with link-layer encryption. Again, this causes the handshake to time out. In the third attack, an adversary waits until the victim completes the 4-way handshake. Then she initiates a rekey by injecting a malformed 4-way handshake messages, causing several implementations to disconnect the client from the network. Finally, we propose countermeasures against our discovered attacks.

Network Protocols, Wi-Fi, 802.11, Denial-of-Service attacks, 4-way handshake