New Technique for a Known Attack Vector

On August 4, 2018, Jens "Atom" Steube, the lead developer of Hashcat, released a forum post disclosing a new technique that attempts to obtain and crack Wi-Fi Protected Access 2 (WPA2) passwords. This is a protocol-level technique carried out on the RSN IE of a single EAPOL frame. The intent is to obtain and crack the pairwise master key sent from a wireless vendor's device that is following the WPA2 specification. The technique can only be carried out with PMKID roaming and WPA2-Personal mode enabled. At this time, no Cisco devices are known to be impacted by this technique. Cisco enterprise wireless products do not support PMKID roaming in WPA2 PSK environments. However, customers should remain vigilant in securing WPA2 against offline dictionary attacks. The companion security advisory will provide additional details if the impact to Cisco devices changes.

Terms to be Familiar With

EAPOL: Extensible Authentication Protocol (EAP) over LAN is a network port authentication protocol used in IEEE 802.1X (Port-Based Network Access Control) developed to give a generic network sign-on to access network resources.

RSN IE: Robust Security Network Information Element is an optional field of variable length that can be found in 802.11 management frames. When it begins to build a secure communication channel, RSN broadcasts an RSN IE message across the network.

PMKID: Pairwise Master Key Identification is a component of RSN and the keying material required to build a connection between a wireless user and an access point. This pairwise master key is what an attacker is attempting to gather to obtain the WPA preshared key.

Offline Dictionary Attack: The attacker tries to guess a Wi-Fi network's password by trying various passwords in quick succession by using a source list of dictionary terms.

Perspectives on WPA2 Protections

While the technique is a new and alternate approach for collecting the inputs for a standard dictionary attack, this does not significantly change the effort required to actually run the attack against WPA2-enabled devices. However, it does serve as a reminder of the importance of choosing strong network passwords that are not susceptible to guessing attempts. Many Cisco products provide a strong password-check feature to aid in this effort.

Cisco continues to advocate securing WPA2 wireless environments using proven 802.1X solutions. The use of IEEE 802.1X offers an effective framework to authenticate and control user traffic to a protected network, as well as to dynamically vary encryption keys. In the Enterprise mode of operation, WPA2 uses 802.1X/EAP for authentication. In addition, 802.1X provides dynamic per-user, per-session encryption keys, removing the administrative burden and security issues surrounding static encryption keys described in the attack technique above. With 802.1X, the credentials used for authentication, such as login passwords, are never transmitted in the clear, or without encryption, over the wireless medium. For more information on 802.1X frameworks and choosing strong passphrases, please refer to the WPA2 + 802.1X WLAN in Cisco Wireless LAN Controller (WLC) Configuration Best Practices.

WPA3 on the Horizon 

With the introduction of WPA3 by the Wi?Fi Alliance, Cisco is delivering soon-to-be-adopted Wi?Fi security with enhanced protections for personal and enterprise networks. WPA3-Personal makes this possible through Simultaneous Authentication of Equals (SAE). As part of the WPA3 standard, SAE adds a secure handshake to resist offline dictionary attacks. More information on SAE and other features of WPA3 is in this Cisco blog post.

Conclusion

Throughout its history, wireless communication has been susceptible to eavesdropping. No matter the WPA standard, there will always be attempts to exploit weaknesses and breach privacy.  Network operators can fortify the networks we rely on daily through proactively securing existing protocols like WPA2, adopting new wireless standards like WPA3, and leveraging proven security practices to ensure data privacy and peace of mind.