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 TCP stack in 4.3BSD Net/2, as used in FreeBSD 5.4, NetBSD possibly 2.0, and OpenBSD possibly 3.6, does not properly implement the session timer, which allows remote attackers to cause a denial of service (resource consumption) via crafted packets.