Sequence Number-Based MAC Address Spoof Detection

The exponential growth in the deployment of IEEE 802.11-based wireless LAN (WLAN) in enterprises and homes makes WLAN an attractive target for attackers. Attacks that exploit vulnerabilities at the IP layer or above can be readily addressed by intrusion detection systems designed for wired networks. However, attacks exploiting link-layer protocol vulnerabilities require a different set of intrusion detection mechanism. Most link-layer attacks in WLANs are denial of service attacks and work by spoofing either access points (APs) or wireless stations. Spoofing is possible because the IEEE 802.11 standard does not provide per-frame source authentication, but can be effectively prevented if a proper authentication is added into the standard. Unfortunately, it is unlikely that commercial WLANs will support link-layer source authentication that covers both management and control frames in the near future. Even if it is available in next-generation WLANs equipments, it cannot protect the large installed base of legacy WLAN devices. This paper proposes an algorithm to detect spoofing by leveraging the sequence number field in the link-layer header of IEEE 802.11 frames, and demonstrates how it can detect various spoofing without modifying the APs or wireless stations. The false positive rate of the proposed algorithm is zero, and the false negative rate is close to zero. In the worst case, the proposed algorithm can detect a spoofing activity, even though it can only detect some but not all spoofed frames.