Firewall ECE-bit bypass

The remote host seems vulnerable to a bug wherein a remote attacker can circumvent the firewall by setting the ECE bit within the TCP flags field. At least one firewall (ipfw) is known to exhibit this sort of behavior. Known vulnerable systems include all FreeBSD 3.x ,4.x, 3.5-STABLE, and 4.2-STABLE.
If you are running FreeBSD 3.X, 4.x, 3.5-STABLE, 4.2-STABLE, upgrade your firewall. If you are not running FreeBSD, contact your firewall vendor for a patch.