Poorly Configured DNSSEC = Potential DDoS Weapon

Just because a domain is signed with DNSSEC security doesn’t mean a Domain Name System (DNS) server is immune to abuse, according to new research.

Neustar studied nearly 1,350 domains with DNSSEC deployed and found that 80% of them could be used to amplify distributed denial-of-service (DDoS) attacks, at an average factor of 28.9 times. That’s because the domains hadn’t properly deployed DNSSEC-signing of their domains, leaving them vulnerable to DDoS abuse. Neustar ran DNS queries from four different open recursive servers to find name servers that responded to queries via the ANY query feature in DNS.

“On average, they returned [responses] 29 times” a normal response, says Joe Loveless, director of security services product marketing at Neustar. “That’s a lot of payback for an attacker who wants amplification.”

Neustar this year also has spotted a large number of actual attacks that take advantage of poorly deployed DNSSEC, he says.

DNS security expert Dan Kaminsky says the real problem lies within DNS, not DNSSEC. “There's a bug, we need to fix it. It's not in DNSSEC and it's kind of not in DNS. We need to be able to track spoofed floods and automate the rate limiting of them,” Kaminsky says.

Neustar’s Loveless concurs with Kaminsky, and adds that it’s more about the administration and deployment of DNSSEC—not its functionality—that’s at risk. “Attackers are exploiting the amplification factors available to them in poorly managed DNSSEC use to create attacks more quickly and more practically,” Loveless says.

Neustar found in its test that the DNSSEC-protected domains in question could be abused to turn an 80-byte query into a 2,313-byte response, which it says could easily could knock a network offline.

DNSSEC signs a domain to provide authentication and verification. The digital signature and key exchange information, in addition to ANY responses, adds up to a bigger amount of traffic than a non-DNSSEC DNS response, according to Neustar. “The record sizes are larger than simple DNS reflection or proper amplification attacks,” Loveless says.

Kaminsky, meanwhile, says there are plenty of amplification attacks against DNS domains that don’t have DNSSEC. “It's called an ANY request because ANY record can be returned, and ANY record can contain ANY information desired by an attacker,” he says.

The Net needs a way to thwart faked traffic sources, says Kaminsky, who is co-founder and chief scientist of WhiteOps.

DDoS threats to DNS are not new. Kaminsky in 2011 blogged that while it’s easy to blame DNSSEC for these flooding DDoS attacks, it’s more of an underlying IP problem of trust and acceptance, and DNS itself is vulnerable to amplification attacks. 

The best defense from DNS DDoS attacks, according to Loveless, is for DNS providers to filter for abuse or not to respond to “ANY” queries. 

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