Distributed Denial of Service (DDoS) Attacks
A Distributed Denial-of-Service (DDoS) attack is one in which a multitude of compromised systems attack a single target, thereby causing denial of service for users of the targeted system. The flood of incoming messages to the target system essentially forces it to shut down, thereby denying service to the system to legitimate users.
In a typical DDoS attack, the assailant begins by exploiting a vulnerability in one computer system and making it the DDoS master. The attack master, also known as the botmaster, identifies and infects other vulnerable systems with malware. Eventually, the assailant instructs the controlled machines to launch an attack against a specified target.
There are two types of DDoS attacks: a network-centric attack which overloads a service by using up bandwidth and an application-layer attack which overloads a service or database with application calls. The inundation of packets to the target causes a denial of service. While the media tends to focus on the target of a DDoS attack as the victim, in reality there are many victims in a DDoS attack -- the final target and as well the systems controlled by the intruder. Although the owners of co-opted computers are typically unaware that their computers have been compromised, they are nevertheless likely to suffer a degradation of service and not work well.
A computer under the control of an intruder is known as a zombie or bot. A group of co-opted computers is known as a botnet or a zombie army. Both Kaspersky Labs and Symantec have identified botnets -- not spam, viruses, or worms -- as the biggest threat to Internet security.
Perpetrators of DoS attacks typically target sites or services hosted on high-profile web servers such as banks, credit card payment gateways, and even root nameservers. DoS threats are also common in business, and are sometimes responsible for website attacks.This technique has now seen extensive use in certain games, used by server owners, or disgruntled competitors on games, such as server owners' popular Minecraft servers. Increasingly, DoS attacks have also been used as a form of resistance. Richard Stallman has stated that DoS is a form of 'Internet Street Protests’. The term is generally used relating to computer networks, but is not limited to this field; for example, it is also used in reference to CPU resource management.
One common method of attack involves saturating the target machine with external communications requests, so much so that it cannot respond to legitimate traffic, or responds so slowly as to be rendered essentially unavailable. Such attacks usually lead to a server overload. In general terms, DoS attacks are implemented by either forcing the targeted computer(s) to reset, or consuming its resources so that it can no longer provide its intended service or obstructing the communication media between the intended users and the victim so that they can no longer communicate adequately.
Denial-of-service attacks are considered violations of the Internet Architecture Board's Internet proper use policy, and also violate the acceptable use policies of virtually all Internet service providers. They also commonly constitute violations of the laws of individual nations.
The United States Computer Emergency Readiness Team (US-CERT) defines symptoms of denial-of-service attacks to include:
- Unusually slow network performance (opening files or accessing web sites)
- Unavailability of a particular web site
- Inability to access any web site
- Dramatic increase in the number of spam emails received—(this type of DoS attack is considered an e-mail bomb)
- Disconnection of a wireless or wired internet connection
- Long term denial of access to the web or any internet services
In the Police and Justice Act 2006, the United Kingdom specifically outlawed denial-of-service attacks and set a maximum penalty of 10 years in prison.
In the US, denial-of-service attacks may be considered a federal crime under the Computer Fraud and Abuse Act with penalties that include years of imprisonment. Many other countries have similar laws.
No comments:
Post a Comment