Sinkholing For Profit

"Sinkholing" is a technique often used by the Internet security community for usurping control of a malicious server from a cybercriminals control. By yanking away control of a domain name associated with a particular threat, security vendors are able to intercept traffic that was destined for the criminal’s original server and direct it to a server the vendor controls.

Instead of the cybercriminal receiving the victim’s stolen personal information or issuing new commands to bot-infected devices, that information (and control capability) essentially becomes accessible to the vendor that operates the sinkhole.

But more and more frequently, people are questioning the legality, if not ethics, of some sinkhole operations.

When cybercriminals seek to launch a new crimeware infection campaign or manage a distributed botnet, they will often employ multiple servers around the world. In order for the crimeware agents to locate and eventually connect to these servers, cybercriminals purchase domain names (e.g., fluffypuppy666.cn) and configure DNS services to resolve host names (e.g., CnC.fluffypuppy666.cn) to their physical server(s). An easy way to disrupt, and ultimately usurp, a crimeware campaign or botnet is for an external entity (e.g. ,a security vendor or law enforcement agency) to approach the domain registrar, prove the level of abuse, and obtain control of the domain name -- and thereby modify DNS resolution settings, which, in turn, allow that entity to control the destination of victim traffic.

Security vendors that gain control of these abused domain names will typically point the DNS entries to a server they themselves control. Any crimeware-infected devices relying on these domain names will thereafter attempt to connect to that security vendor’s server (which is commonly referred to as a sinkhole). Depending on the type of crimeware distributed by the criminal and the configuration of the vendor’s sinkhole, any information lifted from the victim’s computer via the crimeware will automatically be dumped on the vendor’s nominated server, therefore becoming accessible to them. And therein lies the problem.

The information obtained following the sinkholing of an abused domain is often very useful to those charged with protecting parts of the Internet and studying the threat landscape. When you sinkhole the server(s) of a large botnet, you almost instantly gain insight about its size and victim diversity -- just by using the IP address information -- and you can monitor the dynamics of a dying botnet (and extrapolate the efficacy of crimeware remediation tools).

That’s as about as benign as things can get, though. Again, depending on the configuration of the sinkhole server and the capabilities of the vendor controlling it (not to mention scruples), there are several other things that can be done with a “taken-down” botnet. For example:

1) Armed with knowledge of the IP addresses, the vendor can contact the ISPs that manage the victim addresses and get them to alert their customers of the compromise.

2) Similar to (1), but the vendor can sell the current “real time” list of victim IP addresses to banks, online merchants, and other interested parties so that they can, in turn, either alert their own customers to the compromise and/or augment additional back-end fraud detection systems.

3) If the malware type or family is known, then it is possible to deduce the operating system of the victim’s computer. When combined with IP address information, this data is useful to intelligence agencies because it allows organizations to geographically map current and future victim populations.

4) Many crimeware families will steal PII and other configuration information from a victim’s computer, archive it locally, encrypt it, and then upload it to the criminal’s server. This information can be used to uniquely identify the victims of the attack -- without requiring interaction with an ISP. PII, such as credit card details and online banking credentials, are often passed to organizations such as NCFTA -- which, in turn, passes those details on to the relevant financial institutes.

5) Similar to above, but the vendor keeps a copy of the data, extracts key features (such as operating system, patching state, applications, license keys, passwords, etc.), and sells this data to various intelligence agencies.

6) If the vendor is able to replicate the command-and-control (CnC) channel, they are able to take control of the individual botnet victim devices. Access to these systems can then be sold to other remote entities.

For many people, the prospect of some vendor making financial gain from their misfortune is tough to swallow. The thought that their information could be sold to foreign intelligence agencies is downright scary.

It’s a bit like losing your wallet. In the most benign case, some gentleman taps you on your shoulder and points to the wallet you just dropped, or perhaps picks it up and hands it to a nearby police office without looking in it. Alternatively, some less-than-gentlemanly fellow picks up your wallet, rifles through it, takes the cash and any other valuables, and disposes of the wallet. Or worst of all, you have the folks who go hunting for lost wallets with the intent of copying any personal details and selling those details on to others, and then following you around hoping that you’ll eventually drop your car keys or house keys, too.

There is a growing concern within the security community that some vendors are adopting increasingly dubious business practices when it comes to running sinkholes, and monetizing the information they harvest. With the increases in large-scale public botnet takedowns, this is obviously a concern of law enforcement. It’s bad enough being the victim of the original crimeware. Nowadays, you’re never quite sure whether it’s the cybercriminals or foreign intelligence agencies that have your stolen data, or what they’re planning on doing with it next.

Gunter Ollmann is vice president of research at Damballa