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

ipfw(8) is a system facility which provides IP packet filtering, accounting, and redirection. Among the many features, while discarding packets it can perform actions defined by the user, such as sending back TCP reset or ICMP unreachable packets. These operations can be performed by using the reset, reject or uncreach actions. The firewall maintains a pointer to layer 4 header information in the event that it needs to send a TCP reset or ICMP error message to discard packets. Due to incorrect handling of IP fragments, this pointer fails to get initialized.