The remote host is missing an update to the system as announced in the referenced advisory FreeBSD-SA-08:04.ipsec.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-08:04.ipsec.asc

The IPsec suite of protocols provide network level security for IPv4 and IPv6 packets. FreeBSD includes software originally developed by the KAME project which implements the various protocols that make up IPsec. There is an improper reference to a data structure in the processing of IPsec packets, which can result in a NULL pointer being dereferenced.