This weeks DoS attack review will focus on wireless vulnerabilities, specifically as a result of replay attacks. The simple definition of which is:

A network attack whereby valid data transmission is maliciously or fraudulently repeated or delayed

Replays attacks are simple but in many case very effective (source: Fent et al. 2007)

A key article used in this post is: Feng Z., Ning, J., Broustis, I., Pelechrinis, K., Krishnamurthy, S. V., Faloutsos, M.,  2008?, Coping with Packet Replay Attacks in Wireless Networks, US Army Research Office

Replay attacks are particularly effective against wireless networks as the capture and injection of packets is much easier to accomplish as opposed to a wired network. Aireplay-ng is a linux tool that enables replay attacks to be conducted on unprotected wireless network very simply. This tool is used in conjunction with packetforge-ng which allows attackers to easily create new or forged packets for injection. Feng et al. cite network degradation via one terminal against an access point of up to 61%. That degradation is a achieved through unintelligent packet spamming. Also mentioned is the straight forward mitigation strategy of using public key encryption to digitally sign packets although this is indeed a slow process for data comms.

Using packet replay, there are a number of attacks that can be launched:

  • Simplistic packet replay to increase network congestion.
  • De-authentication – This attack sends disassociate packets to one or more clients which are currently associated with a particular access point.

Mitigation strategies:

  • One time passwords
  • Session tokens
  • Random check numbers
  • Timestamping
  • RADIUS [Remote Authentication Dial In User Service] server
  • EAP [Extensible Authentication Protocol]

As per advanced network security lectures this post will focus on analyzing how a RADIUS and EAP prevent replay attacks. The RADIUS protocol documentation lists a Digest-nonce count attribute as does the EAP protocol specification.

Through the handshake process nonce values are used by both the AP and the supplicant to protect against replay attacks:

When using EAP nonce values are used to establish sessions keys safe from replay attacks

I need to do further reading as to the process post key handshake. I would imagine that an encrypted counter could be used to prevent effectivness of replay attacks.