FreeBSD contains a flaw that may allow a malicious user to bypass a firewall. The issue is triggered when ipfw is used with the "me" identifier on a point to point interface. It is possible that the flaw may allow unintended access to the local system by a remote host resulting in a loss of integrity.
Upgrade to version 4.3-STABLE or the RELENG_4_3 security branch after the respective correction dates, as it has been reported to fix this vulnerability. Also, FreeBSD has released a patch.