Network Denial of Service: Reflection Amplification
Adversaries may attempt to cause a denial of service by reflecting a high-volume of network traffic to a target. This type of Network DoS takes advantage of a third-party server intermediary that hosts and will respond to a given spoofed source IP address. This third-party server is commonly termed a reflector. An adversary accomplishes a reflection attack by sending packets to reflectors with the spoofed address of the victim. Similar to Direct Network Floods, more than one system may be used to conduct the attack, or a botnet may be used. Likewise, one or more reflector may be used to focus traffic on the target.
Reflection attacks often take advantage of protocols with larger responses than requests in order to amplify their traffic, commonly known as a Reflection Amplification attack. Adversaries may be able to generate an increase in volume of attack traffic that is several orders of magnitude greater than the requests sent to the amplifiers. The extent of this increase will depending upon many variables, such as the protocol in question, the technique used, and the amplifying servers that actually produce the amplification in attack volume. Two prominent protocols that have enabled Reflection Amplification Floods are DNS and NTP, though the use of several others in the wild have been documented. In particular, the memcache protocol showed itself to be a powerful protocol, with amplification sizes up to 51,200 times the requesting packet.
|Filter Network Traffic||
When flood volumes exceed the capacity of the network connection being targeted, it is typically necessary to intercept the incoming traffic upstream to filter out the attack traffic from the legitimate traffic. Such defenses can be provided by the hosting Internet Service Provider (ISP) or by a 3rd party such as a Content Delivery Network (CDN) or providers specializing in DoS mitigations.
Depending on flood volume, on-premises filtering may be possible by blocking source addresses sourcing the attack, blocking ports that are being targeted, or blocking protocols being used for transport.
As immediate response may require rapid engagement of 3rd parties, analyze the risk associated to critical resources being affected by Network DoS attacks and create a disaster recovery plan/business continuity plan to respond to incidents.
Detection of reflection amplification can sometimes be achieved before the traffic volume is sufficient to cause impact to the availability of the service, but such response time typically requires very aggressive monitoring and responsiveness or services provided by an upstream network service provider. Typical network throughput monitoring tools such as netflow, SNMP, and custom scripts can be used to detect sudden increases in network or service utilization. Real-time, automated, and qualitative study of the network traffic can identify a sudden surge in one type of protocol can be used to detect a reflection amplification DoS event as it starts. Often, the lead time may be small and the indicator of an event availability of the network or service drops. The analysis tools mentioned can then be used to determine the type of DoS causing the outage and help with remediation.
- Marek Majkowsk, Cloudflare. (2017, May 24). Reflections on reflection (attacks). Retrieved April 23, 2019.
- Cloudflare. (n.d.). What is a DNS amplification attack?. Retrieved April 23, 2019.
- Cloudflare. (n.d.). What is a NTP amplificaiton attack?. Retrieved April 23, 2019.
- Philippe Alcoy, Steinthor Bjarnason, Paul Bowen, C.F. Chui, Kirill Kasavchnko, and Gary Sockrider of Netscout Arbor. (2018, January). Insight into the Global Threat Landscape - Netscout Arbor's 13th Annual Worldwide Infrastructure Security Report. Retrieved April 22, 2019.
- Marek Majkowski of Cloudflare. (2018, February 27). Memcrashed - Major amplification attacks from UDP port 11211. Retrieved April 18, 2019.
- Meintanis, S., Revuelto, V., Socha, K.. (2017, March 10). DDoS Overview and Response Guide. Retrieved April 24, 2019.
- Cisco. (n.d.). Detecting and Analyzing Network Threats With NetFlow. Retrieved April 25, 2019.