First things first, IPv6 is a welcomed advancement, but no panacea. Before we even reach the technical security concerns of IPv6, we have to migrate to it first, and this migration may pose some of the biggest security challenges we’ve faced.
Changing from IPv4 to IPv6 means messing with the veins and arteries of the Internet itself. When bridging and transitioning between IPv4 and IPv6, you’re not just considering the specific set of security issues associated with either one you’re considering the security aspects of both. This greatly increases the potential for attacks many of which will be the result of poor, flaw-ridden implementations or misconfigured systems.