The TCP implementation in (1) Linux, (2) platforms based on BSD Unix, (3) Microsoft Windows, (4) Cisco products, and probably other operating systems allows remote attackers to cause a denial of service (connection queue exhaustion) via multiple vectors that manipulate information in the TCP state table, as demonstrated by sockstress.
The system configuration control (sysctl) facility in BSD based operating systems OpenBSD 2.2 and earlier, and FreeBSD 2.2.5 and earlier, does not properly restrict source routed packets even when the (1) dosourceroute or (2) forwarding variables are set, which allows remote attackers to spoof TCP connections.