IPv6 tunneling support is enabled by default and no filtering rules are applied to tunelled traffic.
CVE:
CVE-2007-1338 (The default configuration of the AirPort utility in Apple AirPort Extreme creates an IPv6 tunnel but does not enable the "Block incoming IPv6 connections" setting, which might allow remote attackers to bypass intended access restrictions by establishing IPv6 sessions that would have been rejected over IPv4.)
