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UDP-based Amplification Attacks

 

Systems Affected


Certain UDP protocols have been identified as potential attack vectors:

DNS
NTP
SNMPv2
NetBIOS
SSDP
CharGEN
QOTD
BitTorrent
Kad
Quake Network Protocol

Threat Level

Overview


A Distributed Reflective Denial of Service (DRDoS) attack is an emerging form of Distributed Denial of Service (DDoS) that relies on the use of publicly accessible UDP servers, as well as bandwidth amplification factors, to overwhelm a victim system with UDP traffic.


Description


UDP, by design, is a connection-less protocol that does not validate source IP addresses. Unless the application-layer protocol uses countermeasures such as session initiation, it is very easy to forge the IP packet datagram to include an arbitrary source IP address [7]. When many UDP packets have their source IP address forged to a single address, the server responds to that victim, creating a reflected Denial of Service (DoS) Attack.

Recently, certain UDP protocols have been found to have particular responses to certain commands that are much larger than the initial request. Where before, attackers were limited linearly by the number of packets directly sent to the target to conduct a DoS attack, now a single packet can generate tens or hundreds of times the bandwidth in its response. This is called an amplification attack, and when combined with a reflective DoS attack on a large scale it makes it relatively easy to conduct DDoS attacks.

To measure the potential effect of an amplification attack, we use a metric called the bandwidth amplification factor (BAF). BAF can be calculated as the number of UDP payload bytes that an amplifier sends to answer a request, compared to the number of UDP payload bytes of the request [9] [10]. The list of known protocols, and their associated bandwidth amplification factors, is listed below. US-CERT would like to offer thanks to Christian Rossow for providing this information to us. For more information on bandwith amplificatication factors, please see Christian's blog and associated research paper.


Impact


Attackers can utilize the bandwidth and relative trust of large servers that provide the above UDP protocols to flood victims with unwanted traffic, a DDoS attack.


Solution/ Workarounds


  ✻  Update the latest version of the Mozilla's Firefox on Windows, Linux and Mac.


References


http://www.us-cert.gov/ncas/alerts/TA14-017A


Disclaimer


The information provided herein is on "as is" basis, without warranty of any kind.


 
     

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