A type of distributed denial-of-service attack, DNS amplification, has risen sharply, according to new research from Symantec.
The security vendor said it saw a 183 percent increase in DNS (Domain Name System) amplification attacks from January through August, which abuse recursive DNS resolvers.
Recursive DNS resolvers look up a domain name and return an IP address, which can be called into a browser.
But these types of servers return a large amount of data. Attackers abuse them by making requests but substituting the IP address of their victims.
That directs a large amount of data to the victims, consuming up to 50 times more bandwidth, making it an "amplification" attack.
The problem is that there are 28 million open DNS resolvers, which should be locked down and secured, wrote Symantec's Candid Wueest, a threat researcher, in a report.
"Until this problem is addressed, DNS reflection attacks will continue to be used for large DDoS attacks," he wrote. "In the past, we have also noticed that some attackers set up their own deliberately vulnerable DNS servers and then misused them for reflection attacks."
DDoS attack continue to be a problem, as a variety of groups—from hackers to extortionists—use the method to punish or embarrass companies and organizations.
Most of the DDoS attack traffic for the first half of this year came from India at 26 percent, with the next highest source being the U.S. at 17 percent, Symantec wrote. The reason may be a high number of poorly configured servers that can be abused for amplification attacks.
The most common type of organizations targeted by DDoS flood attacks are those in the gaming industry, then software companies and media organizations.
DDoS have become shorter in duration but tend to focus a larger amount of traffic toward a victim. Larger but shorter attacks follow initial probes that are intended to figure out what defenses are in place.
"In other attacks, small bursts were enough to temporarily disrupt the victim's operations," Wueest wrote. "For example, in online games, a short offline window of a few minutes can be enough to settle the odds on who will win the game."
DDoS attackers were quick to exploit the "Shellshock" flaw, a vulnerability discovered in September in Bash, a command-line shell processor present in most Unix and Linux systems.
"Within 24 hours after news about the ShellShock Bash vulnerability was published, we saw the first use of an exploit against the issue, where attackers aimed to install DDoS malware scripts on Unix servers," Wueest wrote.
DDoS scripts such as PHP.Brobot and Backdoor.Piltabe were installed on vulnerable Unix servers, abusing their high bandwidth for attacks.
The going rate for DDoS hire services—often referred to as "booter" or "stresser" services—range from as little as US$5 to $1,000, charged according to the attack's duration and size.
"These services are commonly offered in the gaming community to temporarily get rid of competing teams," Wueest wrote.