Large Attacks Hide More Subtle Threats In DDoS Data

The massive avalanche of data in March that crashed down on Spamhaus, the maintainer of a number of spam blacklists, made headlines as the largest distributed denial-of-service (DDoS) attack witnessed to date.

Along with the ongoing campaign against financial institutions by a group of attackers calling themselves the Cyber Fighters of Izz ad-din Al Qassam, the attacks drove the bandwidth of the average DDoS to nearly 50 Gbps during the first quarter of 2013, a sevenfold increase over the past three months of 2012, according to a quarterly report by DDoS mitigation firm Prolexic.

Yet those large attacks are not the most significant denial-of-service (DoS) threat for most companies, according to DDoS mitigation experts.

"The big gigabit, the big DNS reflection attacks -- those get all the press, but the ones that are devastating are the ones that knock the application down," says Vann Abernethy, senior product manager for NSFOCUS, a Beijing-based DDoS-mitigation and network-security firm.

While approximately three-quarters of all DoS attacks are bandwidth-clogging floods of network packets, the remaining quarter are application-layer attacks. These attacks can cause far more chaos for companies, taking servers down and requiring greater cleanup efforts than simple infrastructure attacks.

The situation is made more complicated for defenders by the fact that attackers increasingly use data floods to hide low-volume application-layer attacks. Companies need to be able to watch for the attacks, also known as Layer-7 attacks, and be able to detect the trickle of attack packets inside of the much larger infrastructure attacks, says David Fernandez, information security manager for Prolexic's PLXsert security team. Prolexic typically sees about 10 to 15 percent of packet floods hiding a more insidious attack on the target's application.

"Companies should have the ability to isolate the application attacks from the volumetric DDoS," Fernandez says. "There is a pattern in there, and isolating that should be a priority."

The attacks can be differentiated at the packet level, so defending against application-layer attacks means culling as much of the larger attack from the traffic and then inspecting the remaining packets to find those that match the ongoing attack. Needless to say, defending against application-layer attacks takes time and effort, says Dan Holden, director of security research at Arbor Networks, an anti-DDoS technology provider.

"DDoS defense is not a plug-and-play technology," he says. "It is an active defense model. From an application-defense standpoint, you can do things at the application level itself to strengthen the application or disable certain features temporarily."

[Referring to the attacks as "a call to action for the Internet community as a whole," security groups urge organizations to lock down any open DNS resolvers. See Spamhaus DDoS Spotlights DNS Server Security Challenge.]

While companies can rely on service providers or their ISPs to help mitigate infrastructure attacks, application-layer attacks are a different situation, says Holden. The attacks are not a network problem but a business problem, and no one understands a company's business like it does, he says.

"You know more about your application than your ISP is going to, so when it comes to defense, your security team is going to be the best-suited," Holden says.

Finally, companies should not discount the possibility of a massive attack. While high-bandwidth attacks are currently the hallmark of the Cyber Fighters of Izz ad-din Al Qassam, the group is not the only one aiming high. Other groups have managed to exceed the 100-Gbps mark as well, Prolexic's Fernandez says. In the first quarter, nearly a dozen attacks topped 100 Gbps. The biggest attack that Prolexic has witnessed was an attack in April that topped 160 Gbps.

Companies need to do a risk assessment to make sure they can withstand attacks on their businesses, Fernandez says. Companies should expect that they will be targeted with an attack of tens of gigabits per second as well as an application-layer attack, and make sure they are prepared to handle the incident.

"The best measure is to validate what the risk is of certain of your business, and make sure that you can allocate for that," he says.

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