CERT: Denial-of-Service Vulnerabilities in TCP/IP Stacks

A variety of denial-of-service vulnerabilities has been explored and documented by BindView's RAZOR Security Team. These vulnerabilities allow attackers to consume limited resources on victim machines. BindView's RAZOR Security Team has referred to these vulnerabilities as Naptha vulnerabilities. Denial-of-service attacks are possible whenever an attacker can consume a limited resource on a victim's machine. Examples of the kinds of resources that an attacker can consume are CPU time, network bandwidth, and volatile and non-volatile memory. In addition, intruders can also attempt to consume limited data structures such as process slots, open file handles, or other data structures required for the operation of a machine or service.

Recently, BindView's RAZOR Security Team has explored and documented a number of resource exhaustion attacks against TCP/IP services. TCP can be modeled as a finite state machine, consisting of eleven states (CLOSED, LISTEN, SYN RECVD, SYN SENT, ESTABLISHED, CLOSE WAIT, LAST ACK, FIN WAIT-1, FIN WAIT-2, CLOSING, and TIME WAIT) [1]. Implementations of TCP and services that use TCP rely on limited data structures to implement the states of the TCP finite state machine. By attacking specific weaknesses in applications and implementations of TCP, it is possible for an attacker to cause services or systems to crash, refuse service, or otherwise become unstable. A related attack, called a "syn flood attack,"[2] exploited a weakness in how many TCP implementations handled a large number of connections in the "SYN RECVD" state. Naptha attacks exploit weaknesses in the way some TCP stacks and applications handle large numbers of connections in states other than "SYN RECVD," including "ESTABLISHED" and "FIN WAIT-1."