The remote host is missing an update to the system as announced in the referenced advisory FreeBSD-SA-06:07.pf.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-06:07.pf.asc

pf is an Internet Protocol packet filter originally written for OpenBSD. In addition to filtering packets, it also has packet normalization capabilities. A logic bug in pf's IP fragment cache may result in a packet fragment being inserted twice, violating a kernel invariant.