Please note that the same class of attack is possible even if Xauth (Extended Authentication) is used. This is because Xauth is performed after Phase 1 is completed and, for this attack, an adversary
needs only a packet from Phase 1. Furthermore, after the pre-shared key has been discovered, an adversary can mount an active MiTM attack
on Xauth. The outcome depends on the exact authentication method used
in Xauth.
May I ask how this applies to "IKE Shared Secret AAA"? If a Radius backend authenticator is used, is the shared key that is vulnerable one preconfigured in the VPN hosts or one based on the Radius password? The reason I ask is that the preconfigured shared key can easily be lengthened but the backend password, if based on end user passwords, is not as easy a solution. :)
Thank you.
Gary Flynn Security Engineer - James Madison University
