A domain name server (DNS) helps the users to reach a particular website hosted on a particular server. With the advance in technology, the DNS service has been upgraded to dynamic DNS service. The dynamic DNS service helps a domain name to point to Internet resources hosted on changing public IP addresses. However, dynamic DNS service has both advantages and disadvantages just like all other technologies.
On the positive side, the dynamic DNS service helps small scale businesses who need to provide consistent content or services to their customers. These small scale businesses use the IP assigned to them by their ISP, and every time their IP changes, they notify their dynamic DNS provider to update its name servers so that the customer’s domain points now to the new IP.
On the negative side, the dynamic DNS service, especially the free dynamic DNS service, are being abused by cyber criminals for various cyber crimes and cyber attacks. Some of the nefarious activities of cyber criminals abusing dynamic DNS service include malware implants in websites, targeted spear phishing, establishing of C&C for botnet, spamming, etc.
Abusing dynamic DNS service helps the cyber criminals escape the authorship attribution for their cyber crimes. It provides a layer of anonymity and anti forensics to the criminal activities of those abusing dynamic DNS service. This is more so when IP address cannot be solely relied upon to secure a conviction in a cyber crime case.
Further, using dynamic DNS services can also help in bypassing the IP blacklisting deployed by various service providers to prevent DNS abuses. The malware can be continued to be used to infect the computers of end users by using constantly-changing hosting IP addresses.
These IP addresses usually belong to law abiding and innocent users whose computers are compromised and made part of the botnet. These IP addresses may also belong to compromised public websites where the malicious payloads may be installed.
There may be a situation where domains themselves may be blacklisted. To circumvent domain blacklisting, cyber criminals can also use randomly-generated disposable sub-domains under the dynamic DNS domain to point to the next hop in a redirection chain or to the final malware hosting IP.
This behaviour seems similar to fast flux method but in practice dynamic DNS and fast flux are different concepts. Dynamic DNS operates at a micro level whereas fast flux operates at a macro level. Dynamic DNS operates at a regional level whereas fast flux operates at international level. Further, the authoritative name servers for a dynamic DNS domain physically belong to the dynamic DNS provider, whereas with fast flux, double fluxing is possible where the name servers can be made point to constantly changing IP address of physical hosts located in different countries. In practice, dynamic DNS domains map to a much smaller set of IP addresses than fast flux.
So what is the purpose of using the fast flux method? Fast flux is a DNS technique used by cyber criminals to hide phishing and malware delivery sites behind an ever-changing network of compromised hosts (botnets) acting as proxies. It can also refer to the combination of peer-to-peer networking, distributed command and control, web-based load balancing and proxy redirection used to make malware networks more resistant to discovery and counter-measures. Fast flux may be a single-flux or double-flux.
Some of these phishing and malware delivery websites are hosted on bullet proof server with mirrored hosting facilities. Mirrored hosting is a powerful mirrored web hosting management platform that uses multiple specially designed virtual servers to host website with 100% uptime. This is supported by powerful automated control panels. No one is able to trace original IP of the server or the place where the files are hosted so the websites/domains hosted have a 100% Uptime.
The security vendors must have been working on this issue and they may come up with state of the art and innovative methods to deal with this situation.