Insufficient Control of Network Message Volume (Network Amplification)

Description

In the absence of a policy to restrict asymmetric resource consumption, the application or system cannot distinguish between legitimate transmissions and traffic intended to serve as an amplifying attack on target systems. Systems can often be configured to restrict the amount of traffic sent out on behalf of a client, based on the client's origin or access level. This is usually defined in a resource allocation policy. In the absence of a mechanism to keep track of transmissions, the system or application can be easily abused to transmit asymmetrically greater traffic than the request or client should be permitted to.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

This code listens on a port for DNS requests and sends the result to the requesting address.

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.bind( (UDP_IP,UDP_PORT) )
while true:

  data = sock.recvfrom(1024)
  if not data:
    break

  (requestIP, nameToResolve) = parseUDPpacket(data)
  record = resolveName(nameToResolve)
  sendResponse(requestIP,record)

This code sends a DNS record to a requesting IP address. UDP allows the source IP address to be easily changed ('spoofed'), thus allowing an attacker to redirect responses to a target, which may be then be overwhelmed by the network traffic.

See Also