Academic institutions urged to take steps to prevent DNS amplification attacks

Colleges and universities are being encouraged to scrutinize their systems to keep them from being hijacked in DDoS (distributed denial-of-service) attacks.

The Research and Education Networking Information Sharing and Analysis Center (REN-ISAC) advised academic institutions this week to review their DNS (Domain Name System) and network configurations in order to prevent their systems from being abused to amplify DDoS attacks.

"The REN-ISAC wants to raise awareness and drive change concerning common network and domain name system (DNS) configurations that fall short of accepted best practice and which, if left unchecked, open the door for your institution to be exploited as an unwitting partner to crippling denial of service attacks against third parties," said Doug Pearson, technical director of REN-ISAC, in an alert sent Wednesday to the organization's members.

REN-ISAC's members include over 350 universities, colleges and research centers from the U.S, Canada, Australia, New Zealand and Sweden.

The DDoS attacks Pearson refers to are known as DNS amplification or DNS reflection attacks and involve the sending of DNS queries with a spoofed IP (Internet Protocol) address to recursive DNS resolvers that accept queries from outside of their networks.

These spoofed requests result in considerably larger responses sent by the queried "open" DNS resolvers to the IP addresses of the intended victims, flooding them with unwanted traffic.

This attack method has been known for many years and was recently used to launch a DDoS attack of unprecedented scale that reportedly peaked at over 300Gbps against a spam-fighting organization called Spamhaus.

"To put that in context, most universities and organizations connect to the Internet at 1 Gbps or less," Pearson said. "In this incident not only was the intended victim crippled, Internet service providers and security service providers attempting to mitigate the attack were adversely affected."

"The higher education and research community needs to do its part to ensure that we are not helping to facilitate these attacks," Pearson said.

REN-ISAC issued two versions of the alert, one meant for CIOs that contained more general information about the threat, and one directed at IT security staff, as well as network and DNS administrators, containing technical advice on how to mitigate the problem.

The recommendations included configuring recursive DNS resolvers to only be accessible from the organization's networks, enforcing query rate limits for authoritative DNS servers that do need to be queried from external networks and to implement the anti-spoofing network filtering methods defined in IETF's Best Current Practice (BCP) 38 document.

It's admirable that REN-ISAC is taking this step of notifying its members and educating them about this problem, said Roland Dobbins, a senior analyst in the security engineering and response team at DDoS mitigation vendor Arbor Networks. Other industry associations should do so as well, he said.

By their nature, academic institutions tend to be more open with their access policies and haven't necessarily hardened everything to a degree that would ensure their servers can't be abused, Dobbins said. Arbor has seen open DNS resolvers on all kinds of networks including educational ones, that were used to launch DNS reflection attacks, he said.

However, it's important to understand that DNS reflection attacks are only one type of amplification attack, Dobbins said. Other protocols including SMTP (Simple Mail Transfer Protocol) and NTP (Network Time Protocol) can be abused in a similar way, he said.

Securing and properly configuring DNS servers is important, but it's even more important to implement BCP 38, Dobbins said. Anti-spoofing should be applied on all Internet-facing networks so that spoofed packets cannot originate from them. "The closer we get to universal application of BCP 38, the harder it becomes for attackers to launch DDoS amplification attacks of any kind."