DNS amplification and NTP reflection are two big buzz-terms in the modern world of distributed denial-of-service (DDoS) attacks, but when successful defensive measures force those wells to run dry, a lesser-used reflection attack vector, known as Simple Network Management Protocol (SNMP), could take the forefront.
Johannes Ullrich, dean of research with the SANS Technology Institute, told SCMagazine.com in a Monday email correspondence that SNMP, a UDP-based protocol used to read and set the configurations of network devices, hasn't posed as big a threat as DNS and NTP attacks because there are not as many reflectors available as there are for other protocols.
Ullrich said that most network-connected devices support SNMP in some form and, in a Thursday post, opined that it could be the next go-to vector for attackers after he observed a DDoS reflection attack taking advantage of an unnamed video conferencing system that was exposing SNMP.
In this instance, the attacker spoofed a SNMP request to appear to originate from 220.127.116.11, Ullrich said, explaining that the video conferencing system receives the request and then replies back to the IP address with a significant reply.
An 87 byte “getBulkRequest” resulted in a return of 60,000 bytes of fragmented data, Ullrich wrote in the post, adding that the individual reporting the attack observed roughly five megabits per second of traffic.
“The requests are pretty short, asking for a particular item, and the replies can be very large,” Ullrich said. “For example, SNMP can be used to query a switch for a list of all the devices connected to it. SNMP provides replies that can be larger than DNS or NTP replies.”
As people improve configurations, effectively causing those DNS and NTP reflectors to dry up, SNMP could be the attack vector of choice, Ullrich said – a point that John Graham-Cumming, a programmer with CloudFlare, agreed with in a Monday email correspondence with SCMagazine.com.
“I think that attackers will turn to SNMP once other attack methods are thwarted,” Graham-Cumming said. “At the moment it's easy to use NTP and DNS for attacks, so there's no need for SNMP.”
To get a jumpstart defending against this DDoS vector, Graham-Cumming suggested that network operators limit access to the SNMP devices on their networks. Ullrich went so far as to say that SNMP devices should not be exposed to the internet at all. Both experts added that the “community string,” which serves as a password for accepting requests, should not be so obvious.