FreeBSD -- Resource exhaustion in IP fragment reassembly

Problem Description:
A researcher has notified us of a DoS attack applicable
to another operating system. While FreeBSD may not be
vulnerable to that exact attack, we have identified several
places where inadequate DoS protection could allow an
attacker to consume system resources.
It is not necessary that the attacker be able to establish
two-way communication to carry out these attacks. These
attacks impact both IPv4 and IPv6 fragment reassembly.
Impact:
In the worst case, an attacker could send a stream of
crafted fragments with a low packet rate which would consume
a substantial amount of CPU.
Other attack vectors allow an attacker to send a stream
of crafted fragments which could consume a large amount of
CPU or all available mbuf clusters on the system.
These attacks could temporarily render a system unreachable
through network interfaces or temporarily render a system
unresponsive. The effects of the attack should clear within
60 seconds after the attack stops.