The TCP/IP protocol suite has a number of vulnerability and security flaws inherent in the protocols. Those vulnerabilities are often used by crackers for Denial of Service (DOS) attacks, connection hijacking and other attacks. The following are the major TCP/IP security problems:
TCP SYN attacks (or SYN Flooding) ¡§CThe TCP uses sequence numbers to ensure data is given to the user in the correct order. The sequence numbers are initially established during the opening phase of a TCP connection in the three-way handshake. TCP SYN attacks take advantage of a flaw in how most hosts implement TCP three-way handshake. When Host B receives the SYN request from A, it must keep track of the partially opened connection in a "listen queue" for at least 75 seconds and a host can only keep track of a very limited number of connections. A malicious host can exploit the small size of the listen queue by sending multiple SYN requests to a host, but never replying to the SYN&ACK the other host sends back. By doing so, the other host's listen queue is quickly filled up, and it will stop accepting new connections, until a partially opened connection in the queue is completed or times out. This ability to effectively remove a host from the network for at least 75 seconds can be used as a denial-of-service attack, or it can be used to implement other attacks, like IP Spoofing.
IP Spoofing - IP spoofing is an attack used to gain unauthorized access to computers, whereby the attacker sends messages to a computer with a forging IP address indicating that the message is coming from a trusted host. The IP layer assumes that the source address on any IP packet it receives is the same IP address as the system that actually sent the packet -- it does no authentication. Many higher level protocols and applications also make this assumption, so it seems that anyone able to forge the source address of an IP packet could get unauthorized privileges. There are few variations of IP Spoofing such as Blind and Non-blind spoofing, man-in-the-middle- attack (connection hijacking), etc. For details, please read the IP Spoofing section.
Routing attacks ¡§C This attack takes advantage of Routing Information Protocol (RIP), which is often an essential component in a TCP/IP network. RIP is used to distribute routing information within networks, such as shortest-paths, and advertising routes out from the local network. Like TCP/IP, RIP has no built in authentication, and the information provided
in a RIP packet is often used without verifying it. Attacks on RIP change where data goes to, not where it came from. For example, an attacker could forge a RIP packet, claiming his host "X" has the fastest path out of the network. All packets sent out from that network would then be routed through X, where they could be modified or examined. An attacker could also use RIP to effectively impersonate any host, by causing all traffic sent to that host to be sent to the attacker's machine