The remote host is missing an update to the system as announced in the referenced advisory FreeBSD-SA-04:06.ipv6.asc

Upgrade your system to the appropriate stable release or security branch dated after the correction date https://secure1.securityspace.com/smysecure/catid.html?in=FreeBSD-SA-04:06.ipv6.asc

IPv6 is a new Internet Protocol, designed to replace (and avoid many of the problems with) the current Internet Protocol (version 4). FreeBSD uses the KAME Project IPv6 implementation. Applications may manipulate the behavior of an IPv6 socket using the setsockopt(2) system call. A programming error in the handling of some IPv6 socket options within the setsockopt(2) system call may result in memory locations being accessed without proper validation. While the problem originates in code from the KAME Project, it does not affect other operating systems.