The implementation of SYN cookies (syncookies) in FreeBSD 4.5 through 5.0-RELEASE-p3 uses only 32-bit internal keys when generating syncookies, which makes it easier for remote attackers to conduct brute force ISN guessing attacks and spoof legitimate traffic.
Exploitability
AV:NAC:LAu:NImpact
C:PI:PA:N6.4/AV:N/AC:L/Au:N/C:P/I:P/A:N