Hackers are increasingly turning to DNS reflection to amplify the volume of distributed denial of service (DDoS) attacks.
The technique has been known about for years but seldom used in anger, until the debilitating DDoS attack in March that peaked at 300 Gbps against anti-spam organisation Spamhaus and cloud-based DDoS mitigation firm CloudFlare.
DNS reflection attacks involve sending a request for a large DNS zone file to a DNS server, with the details of the request forged so that they appear to come from the IP addresses of the intended victim.
Open public-facing DNS servers respond to the request with a large file. The attackers' requests are only a fraction of the size of the responses, meaning the attacker can effectively amplify his attack by a factor of 100 from the volume of bandwidth they control.
The same sort of technique has been used to run a series of other attacks since, according to Matthew Prince, CloudFlare's chief exec. Traffic of 50-60 Gbps in each attack is becoming typical. The Spamhaus attack illustrated the open DNS server problem; mitigation actions since that attack mean there are less open resources to exploit.
Nonetheless, exploiting open systems to run debilitating attacks remains relatively straightforward, according to Prince: "All you need is 10 lines of code and a lot of patience.”
As well as the high volume attacks, CloudFlare is seeing a growth in smaller but more sophisticated attacks, often targeting online multiplayer games and similar targets.
In one example, gamers turned haters are targeting login credential servers by blitzing them with fake usernames and passwords. The tactic is designed to stop rivals of hackers being able to log back into online games after being turfed off by so-called booters. With rivals unable to log back into the game, hackers can win by default.
Initial "caveman with a club" SYN flood attacks designed to swamp an internet connection are being followed up by more sophisticated app layer attacks against credential servers, Prince explained. He added that, in many ways, DDoS attacks are getting run for much the same reasons IRC flamewars used to take place.
Prolexic, another DDoS mitigation firm, separately announced it had successfully blocked a massive DNS reflection DDoS attack that peaked at 167 Gbps against an unnamed "real-time financial exchange platform" on 27 May.
“This was a massive attack that made up in brute force what it lacked in sophistication,” said Scott Hammack, Prolexic's CEO. “Because of the proactive DDoS defense strategies Prolexic had put in place with this client, no malicious traffic reached its website and downtime was avoided. In fact, the company wasn’t aware it was under attack.”
The DDoS mitigation for this attack was distributed across Prolexic’s four cloud-based scrubbing centres in Hong Kong, London, and the US. Prolexic’s London-based scrubbing center mitigated the majority of the malicious traffic, which peaked at 90 Gbps.
More background info on DNS reflection DDoS attacks can be found in a whitepaper by Prolexic here (registration required). ®