FreeBSD: VID-359e1548-a652-11e8-805b-a4badb2f4699 (CVE-2018-6923): 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.