See also bug 35542 but I would bump severity for this.
We already have IPv6 enabled on Wikimedia but we only gave sysops rights to do range blocks of /64. However with 6to4, holder of an IPv4 address can get an IPv6 range of /48, which renders IP blocking completely useless if vandals know about 6to4.
Version: unspecified
Severity: major
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=35542