FreeBSD Security Advisory FreeBSD-SA-01:32.ipfilter - When matching a packet fragment, insufficient checks were performed to ensure the fragment is valid. In addition, the fragment cache is checked before any rules are checked. Even if all fragments are blocked with a rule, fragment cache entries can be created by packets that match currently held state information. Because of these discrepancies, certain packets may bypass filtering rules. All versions of FreeBSD prior to the correction date, including FreeBSD 3.5.1 and 4.2, contain this problem.