Internet security research firm Team Cymru has begun publishing a four part series explaining the hows and whys of denial of service attacks.
The series plugs a long standing knowledge gap. ISPs, for example, can learn about DDoS attack trends from the likes of Arbor Networks, but if you're running a small online business then it's all very confusing, which is where Team Cymru's research (YouTube channel here) comes in.
An accompanying paper (published here on Monday to coincide with the release of the second video in the series) explains the various types of DDoS attacks (revenge, extortion, disrupting the business of a rival, political protests etc). It outlines the motivations of miscreants and suggests countermeasures.
The topology of the net means that DDoS attacks often cause collateral damage to sites hosted on the same or adjacent systems to an intended target.
DDoS attacks have been around since the the inception of the web, but have evolved over time to become more sophisticated and powerful. Basic ICMP Ping Flood and Smurf attacks, for example, have evolved to take advantage of the power of botnet networks of virus-infected compromised PCs as well as moving on towards more sophisticated fragmented packet (frag) attacks. Tools to automate attacks have also evolved.
Steve Santorelli, a former Detective Sergeant in Scotland Yard's specialist cybercrime unit and Team Cymru's director of global outreach, explained that, as with many aspects of the underground economy, there's a constant battle between network defenders and ne'er-do-wells trying to circumvent countermeasures that the IT security community develops.
"The automation of attacks, spoofing and the rise in the number of infected clients available as well as the ease with which HTTP based botnets can be created have all contributed to the evolution in sophistication of DDoS attacks," he explained.
Other newer types of attacks take advantage of misconfigured DNS Servers to bombard targeted systems with multiple bogus requests. These so-called DNS Amplification attacks might be launched without the need to gain access to a zombie network.
Mitigation against attacks involves applying filters that drop packets associated with an attack. Team Cymru runs a service that alerts ISPs if misconfigured DNS servers are found on their network.
Unfortunately attackers often monitor and adjust their attacks to use different port and packet size, so repelling determined assaults can become something of a battle of wits. The judicious use of firewalls (to block UDP Floods) and defensive router settings can blunt the impact of some types of attack.
Team Cymru suggests that cybercrooks have moved away from running denial of service attacks towards alternative methods of making an illicit buck. Nonetheless, the assaults remain a huge problem.
"The perception is that DDoS attacks are less favored in the underground economy these days," Santorelli explained. "The underground economy is now almost entirely about profit and DDoS attacks are hard to monetise - given the same amount of time and expertise, commensurately greater profit and less risk can be had with any number of alternate criminal enterprises.
"Large DDoS attacks are more likely to elicit a formal law enforcement investigation than something like spyware or spam. The risk vs reward equation is therefore entirely different.
"To actually make money with DDoS attacks, you also often need to involve folks who are not part of your usual miscreant circle and that entails more risk of detection and that the scheme will fail at some point." ®