Flux node agents share the most essential and basic capabilities of the traditional, but minimalist IRC-based bot in several ways: they regularly phone home to announce their continued availability, they check for updates, perform download operations, and allow for the execution of arbitrary commands on the local operating system by a remote attacker. However, almost without exception, fast-flux Command and Control (C&C) activity observed in the wild thus far has been HTTP protocol based.
The ability of Fast-flux agents to proxy or redirect TCP services appears to be an outgrowth from the redirect functions of legacy IRC bots that possess optional UDP proxy or redirect capabilities. The bundling of these features enables a fast-flux service network to become a powerful criminal tool and helps to make the fast-flux service network operator less easily detectable. The fast-flux front end nodes will either act on command or execute hard-coded instructions to redirect inbound traffic received on configured ports to a specifically chosen upstream fast-flux mothership node. Several fast-flux service network operations have been observed maintaining distributed nodes that act primarily in performing availability and connection quality tests of individual flux-agents within the fast-flux service network. For an example of the development cycle of fast-flux malware, refer to Appendix A. For an example of the infection process for the malware, refer to Appendix B. Below we summarize two commonly used malware that have adopted fast-flux capabilities.
The networks based upon these malware variants have been erected to provide a robust platform for sending large volumes of unsolicited email (spam). They have been very successful in this goal and employ advanced techniques such as the constant automated creation of many malware variants to frustrate anti-virus signature creation. Infected machines download these updates on a regular schedule in order to increase the amount of time it takes for a system to be cleaned and taken offline. These updates must be hosted on websites, so if their public IP addresses remain static, the update sites can potentially be taken down fairly easily. Until recently, a strategy of auto-generating pseudo-random domain names which moved around was used to protect such download sites. Starting in May 2007, the criminal organization behind this spam business moved to a fast-flux service network model. This group is now hosting their DNS services and malware download sites via fast-flux service networks and appear to be enjoying continued success in their criminal endeavor.
The biggest competitor of the Warezov/Stration gang is perhaps the criminal organization operating a very large spam sending network based on the family of malware variants dubbed Storm/Peacomm/Peed. They employ a UDP-based P2P model for botnet command and control. This is a highly robust way to operate a large distributed network if the complexities of managing peer lists and minimizing latency can be overcome. They have also employed novel techniques to counter anti-spam solutions, such as generating image-based spam on the fly on the endpoints flux-agent nodes themselves, rather than simply relying on template based messaging. These images are randomized in ways which frustrate the OCR (object character recognition) technologies used in some anti-spam products and have been most commonly used to facilitate fraudulent pump and dump stock spam schemes. In June 2007 this group was observed attempting to modify their P2P network to support fast-flux style networking. This is a significant advance for spam-sending malware and requires further study.