On May 30, 2014, law enforcement officials from the FBI and Europol seized a series of servers that were being used to help operate the GameOver Zeus botnet, an especially pernicious and troublesome piece of malware. The authorities also began an international manhunt for a Russian man they said was connected to operating the botnet, but the most significant piece of the operation was a side effect: the disruption of the infrastructure used to distribute the CryptoLocker ransomware.
The takedown was the result of months of investigation by law enforcement and security researchers, many of whom were collaborating as part of a working group that had come together to dig into CryptoLocker’s inner workings. The cadre of researchers included reverse engineers, mathematicians and botnet experts, and the group quickly discovered that the gang behind CryptoLocker, which emerged in 2013, knew what it was doing. Not only was the crew piggybacking on the GameOver Zeus infections to reach a broader audience, but it also was using a sophisticated domain-generation algorithm to generate fresh command-and-control domains quickly. That kept the CryptoLocker crew ahead of researchers and law enforcement for a time.
“The interesting thing is all the opsec involved in this. The architecture thought out with this was really clear. The people working on this really sat down and architected and then engineered something,” said Lance James of Deloitte & Touche, who spoke about the takedown effort at Black Hat last year. “It took a lot more people on our side to hit it harder.”
CryptoLocker has become the poster child for a new wave of threats that are designed to relieve victims of their money through the threat of losing all of their files. The malware, like its descendants Cryptowall, Critroni, Crowti and many others, encrypt the contents of victims’ PCs and demands a payment, usually in Bitcoin, in order to get the decryption key. Millions of victims have been hit by these threats in the last couple of years, but putting a number on infections and a dollar value on how much money the crews are making is difficult. However, with ransom payments ranging from less than $100 to as much as $300 or more, the criminals behind these ransomware families are building multimillion dollar businesses on the fear and desperation of their victims.
Despite the sudden appearance of CryptoLocker and the other more recent kinds of ransomware, the concept itself is not new. As far back as the late 1980s, early versions of crypto ransomware were showing up and security researchers began looking at the problem by the mid-1990s. By the mid-2000s, more and more crypto ransomware variants were popping up, but it wasn’t until CryptoLocker reared its head in 2013 that the scope and potential damage of the threat came into sharp focus. Victims, researchers and law enforcement soon realized that the game had changed.
“Just imagine the scale of how many people are being held for ransom with these threats. It’s mind-boggling,” said Anup Ghosh, CEO of security vendor Invincea, which has done research on ransomware threats. “It’s someone else’s problem until your own personal information gets encrypted and you can’t access your work data and photos. The personal pain is so much more dramatic than any other intrusion.”
For all the attention that CryptoLocker and Cryptowall and the other variants have gotten from the media and security researchers, enterprises haven’t yet totally caught on to the severity of the threat. Much of the infection activity by crypto ransomware has targeted consumers thus far, as they’re more likely to pay the ransom to get their data back. But Ghosh said that’s likely to change soon.
“It’s not even on their radar. It’s similar to banking Trojans in terms of what IT guys think of it,” Ghosh said. “They treat it as an individual problem and as a reason to slap people on the wrist. ‘Oh, you must have done something bad’.”
Ransomware gangs use a variety of methods to infect new victims, including riding shotgun on other malware infections and through drive-by downloads. But perhaps the most common infection method is through spam messages carrying infected attachments. These often look like FedEx shipping notifications or fake invoices. When a user opens the attachment, the malware infects the machine and encrypts the files.
But the crypto ransomware gangs don’t operate on their own. They have support systems, developers and other systems in place to help them create their malware and cash out the profits.
“CryptoLocker and GameOver Zeus were often installed alongside each other, and now you see these groups improving from there and specializing,” said John Miller, manager, ThreatScape cyber crime, at iSIGHT Partners. “There’s so much momentum behind ransomware operations and the black markets that support it, we expect it to be a problem for the foreseeable future. There are people selling ransomware, customization services for countries and distribution services for getting it onto machines or phones.”
How much money is involved? Millions and millions of dollars. In just the first six months of operation, the Cryptowall malware generated more than a million dollars in revenue for its creators, according to research from Dell SecureWorks. That’s one group using one variant of crypto ransomware. And there are dozens, if not hundreds, of other groups running similar operations.
Where CryptoLocker innovated with the use of strong encryption and demand for Bitcoin as ransom, other groups have taken the concept and run with it. The Critroni, or CTB-Locker, ransomware not only accepts Bitcoin, but it also uses elliptic curve cryptography and employs the Tor network for command-and-control. The group behind Cryptowall also goes to some lengths to ensure that the ransomware is on the right kind of machine before it runs.
“They went through a lot of work to hide the executable in encryption, to check if it’s running in a virtual machine, and the ability to exploit multiple environments,” said Cisco Talos security research engineer Earl Carter. “So much was put into Cryptowall 2.0. Someone went to a lot of work on the front end to avoid detection.”
The piles of money and growing complaints from victims has begun to draw the attention of law enforcement, as evidenced by the GameOver Zeus-CryptoLocker takedown and actions against the Reveton ransomware operation. Researchers expect the level of law enforcement interest to grow, especially as ransomware infects more enterprises and the profits for attackers continue to grow.
“Now that it’s become apparent how much damage ransomware is causing, law enforcement is paying attention,” Miller said. “It’s gotten their attention in a big way. It’s in their scope. But it hasn’t been targeted very much by takedown activity. A lot of the criminals operating this feel that because what they’re doing is stealing virtual currency from individuals it’s less likely to see law enforcement attention.
“The biggest reason this environment will change is sustained law enforcement action.”