Denial of Service

A denial-of-service (DoS) attack occurs when legitimate users are unable to access information systems, devices, or other network resources due to the actions of a malicious cyber threat actor. Services affected may include email, websites, online accounts (e.g., banking), or other services that rely on the affected computer or network. A denial-of-service condition is accomplished by flooding the targeted host or network with traffic until the target cannot respond or simply crashes, preventing access for legitimate users. DoS attacks can cost an organization both time and money while their resources and services are inaccessible.

What are common denial-of-service attacks?

There are many different methods for carrying out a DoS attack. The most common method of attack occurs when an attacker floods a network server with traffic. In this type of DoS attack, the attacker sends several requests to the target server, overloading it with traffic. These service requests are illegitimate and have fabricated return addresses, which mislead the server when it tries to authenticate the requestor. As the junk requests are processed constantly, the server is overwhelmed, which causes a DoS condition to legitimate requestors.

In a Smurf Attack, the attacker sends Internet Control Message Protocol broadcast packets to a number of hosts with a spoofed source Internet Protocol (IP) address that belongs to the target machine. The recipients of these spoofed packets will then respond, and the targeted host will be flooded with those responses.
A SYN flood occurs when an attacker sends a request to connect to the target server but does not complete the connection through what is known as a three-way handshake—a method used in a Transmission Control Protocol (TCP)/IP network to create a connection between a local host/client and server. The incomplete handshake leaves the connected port in an occupied status and unavailable for further requests. An attacker will continue to send requests, saturating all open ports, so that legitimate users cannot connect.

Individual networks may be affected by DoS attacks without being directly targeted. If the network’s internet service provider (ISP) or cloud service provider has been targeted and attacked, the network will also experience a loss of service.

What is a distributed denial-of-service attack?

A distributed denial-of-service (DDoS) attack occurs when multiple machines are operating together to attack one target. DDoS attackers often leverage the use of a botnet—a group of hijacked internet-connected devices to carry out large scale attacks. Attackers take advantage of security vulnerabilities or device weaknesses to control numerous devices using command and control software. Once in control, an attacker can command their botnet to conduct DDoS on a target. In this case, the infected devices are also victims of the attack.

While there is no way to completely avoid becoming a target of a DoS or DDoS attack, there are proactive steps administrators can take to reduce the effects of an attack on their network.

It is also important to take steps to strengthen the security posture of all of your internet-connected devices in order to prevent them from being compromised.