Understanding IDS Screens for Network Attack Protection

The attacker sends ICMP request probes (pings) to multiple targets. If a target machine replies, the attacker receives the IP address of the target.

The attacker floods a target machine by sending a large number of ICMP packets from one or more source IP addresses. The target machine uses up its resources as it attempts to process those ICMP packets, and then it can no longer process valid traffic.

The attacker sends TCP SYN packets from one source to multiple destination ports of the target machine. If the target replies with a SYN-ACK from one or more destination ports, the attacker learns which ports are open on the target.

The attacker floods a target machine by sending a large number of TCP SYN packets from one or more source IP addresses. The attacker might use real source IP addresses, which results in a completed TCP connection, or might use fake source IP addresses, resulting in the TCP connection not being completed. The target creates states for all the completed and incomplete TCP connections. The target uses up its resources as it attempts to manage the connection states, and then it can no longer process valid traffic.

The attacker floods a target machine by sending a large number of UDP packets from one or more source IP addresses. The target machine uses up its resources as it attempts to process those UDP packets, and then it can no longer process valid traffic.

The attacker sends the target ICMP packets that are IP fragments. These are considered suspicious packets because ICMP packets are usually short. When the target receives these packets, the results can range from processing packets incorrectly to crashing the entire system.

Malformed ICMPv6 packets can cause damage to the device and network. Examples of malformed IPv6 packets are packets that are too big (message type 2), that have the next header set to routing (43), or that have a routing header set to hop-by hop.

The attacker sends the target ICMP frames with an IP length greater than 1024 bytes. These are considered suspicious packets because most ICMP messages are small.

The attacker sends the target ICMP ping packets whose IP datagram length (ip_len) exceeds the maximum legal length (65,535 bytes) for IP packets, and the packet is fragmented. When the target attempts to reassemble the IP packets, a buffer overflow might occur, resulting in a system crashing, freezing, and restarting.

The attacker sends the target packets with incorrectly formatted IPv4 options or IPv6 extension headers. This can cause unpredictable issues, depending on the IP stack implementation of routers and the target.

IP fragments might contain an attacker's attempt to exploit the vulnerabilities in the packet reassembly code of specific IP stack implementations. When the target receives these packets, the results can range from processing the packets incorrectly to crashing the entire system.

Attackers can maliciously use extension headers for denial-of-service attacks or to bypass filters.

Attackers can maliciously use IPv4 options for denial-of-service attacks.

The attacker sends the target fragmented IP packets that overlap. The target machine uses up its resources as it attempts to reassemble the packets, and then it can no longer process valid traffic.

The attacker sends the target packets with protocol numbers greater than 137 for IPv4 and 139 for IPv6. An unknown protocol might be malicious.

The attacker sends the target TCP packets that have the FIN bit set but have the ACK bit unset. This can allow the attacker to identify the operating system of the target or to identify open ports on the target.

The attacker sends the target spoofed SYN packets that contain the target’s IP address as both the destination and the source IP address. The target uses up its resources as it repeatedly replies to itself. In another variation of the land attack, the SYN packets also contain the same source and destination ports.

The attacker initiates Telnet or FTP connections with the target without completing the connections. The target’s session table can fill up, resulting in the device rejecting legitimate connection requests.

The attacker sends the target TCP packets that have both the SYN and the FIN bits set. This can cause unpredictable behavior on the target, depending on its TCP stack implementation.

The attacker sends the target SYN packet fragments. The target caches SYN fragments, waiting for the remaining fragments to arrive so it can reassemble them and complete the connection. A flood of SYN fragments eventually fills the host’s memory buffer, preventing valid traffic connections.

The attacker sends the target TCP packets containing no flags. This can cause unpredictable behavior on the target, depending on its TCP stack implementation.

The attacker sends a TCP segment with the urgent (URG) flag set and destined for port 139 of a target running Windows. This might cause the target machine to crash.