A Mercenary Approach To Botnets

For a period of two years, if often felt that not a week went by without some security company or product vendor announcing the takedown of a multimillion-node botnet. I don't know if it was the waning enthusiasm of the media to cover "yet another botnet takedown," the public's exhaustion over a threat they could do little prevent, or the fact that the majority of botnet "takedowns" were merely temporary setbacks for their criminal overlords, but as we reach the end of 2013, the frequency of such boastings have declined noticeably.

While the public broadcasts of botnet takedowns are now more likely to be associated with a golden age in the battle against the bots, the war continues on a less visible plane. Regardless of whether this war can, in fact, be won, a question I'm increasingly being asked is whether certain organizations and government entities actually want to win it.

Why wouldn't the good guys want to win the botnet battle? Many salty dogs of the security industry have experienced how shutting down one attack vector forces the threat to evolve in another direction -- a direction that will likely be even more difficult to combat or, minimally, require substantial research effort to investigate. Eighty percent efficacy against a threat you understand is considerably better than 0 percent of a threat you have no technology in your back pocket for.

But that’s not the only reason why a growing pool of security professionals would sooner hold back from shutting down the botnets that plague the Internet. Botnets harvest a lot of data from their victims. Access to that data is increasingly lucrative and, if you package the data just right, can be sold on as a subscription feed to a growing pool of organizations.

The security analyst community used to be quite open in the way they shared information about botnets -- in particular, information about the command-and-control (C&C) servers, the domain names and IP addresses being used, samples of the bot malware, and copies of the C&C software. Now, because this information has a demonstrable value, those that have it are much less likely to "give back to the community." If anything, they're more likely to create new subscription services and provide it as a paid-for stream of data.

But what is this data, and who is it useful to?

When people first hear that botnet data is up for sale, I think most jump to the conclusion that the data is a stream of all of the personal and confidential information being stolen from the botnet victims. In some cases it may be, but most often it's not. More often than not, it may simply be a list of IP addresses of the victims under the control of a single piece of malware.

Depending on who you're selling to and what their missions are, even data as "uninteresting" as the IP addresses of the victims holds a unique and complementary value to some folks. For example, government agencies such as the CIA or NSA can use it to map which botnets are successfully penetrating computers within countries or institutions they're tracking. By knowing what the original malware was, the agency is going to know the operating system and major application version numbers of the infected devices. This adds to the pool of knowledge about an adversary, which could be leveraged in a time of need.

If an organization is smart, it'll also be sinkholing the C&C domains -- probably not all of them, just enough to provide visibility of the victims, but not crossing a threshold that forces the criminal who built the botnet to change tactics and stop growing the botnet.

If the botnet C&C software isn't particularly well-written (which is often the case), or if someone has reverse-engineered the C&C portal software and found interesting vulnerabilities, then simply knowing the domain names used by the botnet malware could allow an agency to access all the information being harvested by the bot on the victims computer (e.g., UIDs, passwords, applications installed, browser history, banking credentials, etc.), or even issue new commands.

It used to be that the worlds of bug hunters and malware analysts were separate and far between. In the past couple of years, the ability to analyze malware samples and identify exploitable vulnerabilities in them has become very important. Given that some botnets have a bigger pool of victims than many commercial software vendors have licensed customers, the value of an exploit that grants reliable remote control of a popular malware agent is rising in value. I'd hazard a guess that a remotely exploitable vulnerability in Zeus, SpyEye, or any of the other top10 botnet malware families is likely worth tens of thousands of dollars to most government agencies around the world.

In many ways, botnets have become a golden goose to those charged with gathering intelligence on the populations of foreign entities. The bulk of the victim's data is useful for mapping populations, communication profiles, and as egress points for counterintelligence exercises. Then, given how many botnet victims there are, the probability that a few "interesting" computers will have succumbed along the way is similarly high -- providing direct insight in to a pool of high value targets.

The incentives are high for many businesses and government agencies to not be too heavy-handed in combating the global botnet pandemic. There's money to be had and, with each passing day, more interesting ways are being uncovered in how to package the data, and how to employ it.

-- Gunter Ollmann, CTO, IOActive Inc.