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11/27/2012
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Evolving DDoS Attacks Force Defenders To Adapt

Distributed denial-of-service attacks get bigger and combine application-layer exploits, requiring defenders to be more agile

In the past, attackers using distributed denial-of-service (DDoS) attacks to take down websites or network servers typically adopted one of two tactics: flooding the site with a deluge of data, or overwhelming an application server with seemingly valid requests.

Companies concerned about denial-of-service (DoS) attacks have generally focused more on mitigating data floods, also known as volumetric or infrastructure attacks. Yet, increasingly, attackers are employing a hybrid approach, using multiple vectors to attack. The attacks that hit financial firms in September and October, for example, often used a massive flood of data packets that would overwhelm a victim's network connection, while a much smaller subset of traffic would target vulnerable applications functions, consuming server resources.

"It is almost like sending a whole squadron of tanks and then have an assault team that can go in and be more stealthy in taking out their targets," says Carlos Morales, vice president of global sales engineering and operations for network protection firm Arbor Networks. "It broke the model that people had for stopping these things."

The one-two punch is potent. Many financial firms thought they had defenses in place to defeat such attacks, but had problems staying accessible during the onslaught. Companies prepared to handle application-layer attacks or smaller volumetric attacks could not handle the 20 Gbps or more that saturated their Internet connections. Even a gateway that can keep up with a 10-Gbps connection speed cannot deal with twice as much -- or more -- traffic sent to the same server.

[The distributed denial-of-service (DDoS) attacks that caused disruptions at major banks did not emanate from the widespread home computers of hacktivists, but from hundreds to thousands of servers running vulnerable content management software. See Serious Attackers Paired With Online Mob In Bank Attacks.]

A recent report from network-security firm Prolexic found that the average attack bandwidth had increased to nearly 5 Gbps, with 20-Gbps attacks quite common. In a year, the average volume of attacks had doubled, the firm found.

"The late Sen. Ted Stevens got mocked for saying that the Internet is a 'series of tubes,'" says Matthew Prince, CEO of Cloudflare, a content-delivery and network-security firm. "But the Internet is a series of tubes, and you can only fit so much through it."

Companies must start creating a multilayered approach to stopping DDoS attacks, according to mitigation experts. The greatest amount of attack volume should be stopped inside of a provider's network, away from the company's links to the Internet. Trying to overprovision your network for the worst-case scenario will likely not work and will be very expensive, to boot.

"Even if you are a large bank in the U.S., you are doing less than 10 Gbps of traffic across all the properties of your network combined," Cloudflare's Prince says. "If you have to overprovision that by 10x, that is wasting a lot of resources."

By using a service provider to filter out most of the spurious traffic at the edge of the Internet, companies can pay attention to the data that actually enters their networks. Collecting information on the traffic can help a company to better develop defenses for future attacks as well, even if a company does not have the resources to identify attacks in real time.

Yet faster detection and more agile response can mean the difference between successful defenses and downtime.

"Seeing an impact and understanding that there is an attack happening is not necessarily going to happen at the same time," says Neal Quinn, chief operating officer for attack-mitigation service Prolexic.

For many companies, the threat of attacks is not over, but, rather, just beginning. The most recent attacks did not start with the financial industry; other industries have been hit by similar attacks for almost the past year. Companies should not expect it to end there, either. The holiday season tends to be a popular time for attackers to attempt to extort money from retailers by threatening DoS attacks.

"It is traditionally a very busy time of year for these attacks," Quinn says. "If anything, organizations should make themselves more aware of how well they can handle these attacks."

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