There are various inevitable attacks in networks, such as compromise or sabotage of servers, sensitive data theft, service intervention, or even direct network device sabotage that causes service anomaly or interruption. Security gates, belonging to a category of network security devices, must be designed with attack defense functions to detect various types of network attacks, and take appropriate actions to protect the Intranet against malicious attacks, thus assuring the normal operation of the Intranet and systems.
Devices provide attack defense functions based on security zones, and can take appropriate actions against network attacks to assure the security of your network systems.
ICMP Flood and UDP Flood
An ICMP Flood/UDP Flood attack sends huge amounts of ICMP messages (such as ping)/UDP packets to a target within a short period and requests for a response. Due to the heavy load, the attacked target cannot complete its normal transmission task.
LAN transmits network traffic based on MAC addresses. ARP spoofing attacks occur by filling in the wrong MAC address and IP address to make a wrong corresponding relationship of the target host's ARP cache table. This will lead to the wrong destination host IP packets, and the packet network's target resources will be stolen.
Due to resource limitations, a server will only permit a certain number of TCP connections. SYN Flood just makes use of this weakness. During the attack an attacker will craft a SYN packet, set its source address to a forged or non-existing address, and initiate a connection to a server. Typically the server should reply the SYN packet with SYN-ACK, while for such a carefully crafted SYN packet, the client will not send any ACK for the SYN-ACK packet, leading to a half-open connection. The attacker can send large amount of such packets to the attacked host and establish are equally large number of half-open connections until timeout. As a result, resources will be exhausted and normal accesses will be blocked. In the environment of unlimited connections, SYN Flood will exhaust all the available memory and other resources of the system.
A WinNuke attack sends OOB (out-of-band) packets to the NetBIOS port (139) of a Windows system, leading to NetBIOS fragment overlap and host crash. Another attacking vector is ICMP fragment. Generally an ICMP packet will not be fragmented; so many systems cannot properly process ICMP fragments. If your system receives any ICMP fragment, it's almost certain that the system is under attack.
IP Address Spoofing
IP address spoofing is a technology used to gain unauthorized access to computers. An attacker sends packets with a forged IP address to a computer, and the packets are disguised as if they were from a real host. For applications that implement validation based on IP addresses, such an attack allows unauthorized users to gain access to the attacked system. The attacked system might be compromised even if the response packets cannot reach the attacker.
IP Address Sweep and Port Scan
This kind of attack makes a reconnaissance of the destination address and port via scanners, and determines the existence from the response. By IP address sweeping or port scanning, an attacker can determine which systems are alive and connected to the target network, and which ports are used by the hosts to provide services.
Ping of Death Attack
Ping of Death is designed to attack systems by some over-sized ICMP packets. The field length of an IP packet is 16 bits, which means the max length of an IP packet is 65535 bytes. For an ICMP response packet, if the data length is larger than 65507 bytes, the total length of ICMP data, IP header (20 bytes) and ICMP header (8 bytes) will be larger than 65535 bytes. Some routers or systems cannot properly process such a packet, and might result in crash, system down or reboot.
Teardrop attack is a denial of service attack. It is a attack method based on morbid fragmented UDP packets, which works by sending multiple fragmented IP packets to the attacker (IP fragmented packets include the fragmented packets of which packet, the packet location, and other information). Some operating systems contain overlapping offset that will crash, reboot, and so on when receiving fragmented packets.
Smurf attacks consist of two types: basic attack and advanced attack. A basic Smurf attack is used to attack a network by setting the destination address of ICMP ECHO packets to the broadcast address of the attacked network. In such a condition all the hosts within the network will send their own response to the ICMP request, leading to network congestion. An advanced Smurf attack is mainly used to attack a target host by setting the source address of ICMP ECHO packets to the address of the attacked host, eventually leading to host crash. Theoretically, the more hosts in a network, the better the attacking effect will be.
A fraggle attack is basically the same with a smurf attack. The only difference is the attacking vector of fraggle is UDP packets.
During a Land attack, an attacker will carefully craft a packet and set its source and destination address to the address of the server that will be attacked. In such a condition the attacked server will send a message to its own address, and this address will also return a response and establish a Null connection. Each of such connections will be maintained until timeout. Many servers will crash under Land attacks.
IP Fragment Attack
An attacker sends the victim an IP datagram with an offset smaller than 5 but greater than 0, which causes the victim to malfunction or crash.
IP Option Attack
An attacker sends IP datagrams in which the IP options are abnormal. This attack intends to probe the network topology. The target system will break down if it is incapable of processing error packets.
Huge ICMP Packet Attack
An attacker sends large ICMP packets to crash the victim. Large ICMP packets can cause memory allocation error and crash the protocol stack.
TCP Flag Attack
An attacker sends packets with defective TCP flags to probe the operating system of the target host. Different operating systems process unconventional TCP flags differently. The target system will break down if it processes this type of packets incorrectly.
DNS Query Flood Attack
The DNS server processes and replies to all DNS queries that it receives. A DNS flood attacker sends a large number of forged DNS queries. This attack consumes the bandwidth and resources of the DNS server, which prevents the server from processing and replying legal DNS queries.
TCP Split Handshake Attack
When a client establishes TCP connection with a malicious TCP server, the TCP server will respond to a fake SYN packet and use this fake one to initialize the TCP connection with the client. After establishing the TCP connection, the malicious TCP server switches its role and becomes the client side of the TCP connection. Thus, the malicious traffic might enter into the intranet.