Security professionals generally spend their lives playing defense against adversaries that are not only anonymous, but often invisible. It’s a rare event when hackers and malware authors have their operations curtailed, shutdown or even impacted by members of the infosec community… and even more rare when the community can get an inside look at the infrastructure running these campaigns. That’s why today’s announcement — disclosing Talos Research Group’s work to disrupt the operations of an international ransomware campaign and compromise the infrastructure of one of the most effective methods for distributing malicious software around the world — is so significant.

The Angler exploit has been linked to several high­-profile ransomware campaigns, including both CryptoWall and TeslaCrypt. Angler is widely recognized as one of the most advanced and exploit kits on the market — making the information Talos disseminated all the more important for analysts and engineers who are working to protect their company systems from attacks.

Graph of Angler exploit kit network connections, courtesy of OpenDNS Security Labs

Graph of Angler exploit kit network connections, courtesy of OpenDNS Security Labs

Detailing the takedown in a report on the Cisco Security blog, Talos was able to disrupt the operations of a threat actor responsible for up to 50 percent of the malicious software’s activity from a ransomware campaign that generated more than $30M USD annually. Based on the Angler servers Talos observed, this one actor targeted up to 90,000 victims every day. More than 60 percent of the infections delivered either CryptoWall 3.0 or TeslaCrypt 2.0 ransomware, both variants that have been discussed previously on the OpenDNS Security Labs blog.

But beyond simply sinkholing the domains or shutting down the servers, Talos worked with service provider Limestone Networks to obtain live disk images of the Angler servers. This collaboration allowed Talos researchers to observe the attack campaigns in action, providing valuable information not only on how Angler’s handlers hid their operations from security researchers, but how they architected their infrastructure to ensure maximum effectiveness.

Angler Infrastructure: More than Meets the Eye

One of the most interesting new technical findings from Cisco’s in-depth analysis of the Angler servers was the use of proxies to shield the rest of the exploit infrastructure from investigation. According to Talos’s full report, a single health server was seen monitoring 147 proxy servers over the span of a month. As the report’s authors explain, these proxy servers allow the adversaries “to quickly pivot and change while still shielding the exploit server from identification and exposure.”

OpenDNS CTO Dan Hubbard explained that the practice of using proxy servers is not yet widespread, but it does reflect a trend towards the increased sophistication of so-called “commodity” attack campaigns. “Inevitably, you have to get the data collated somewhere and if that server gets taken away, then that’s the end of it,” he said. “As a result, we’re seeing criminals build up these sophisticated proxy networks so they can scale linearly, much like a CDN or a real web service. Not only can any of these proxies be taken down without affecting service, but it allows them to obfuscate their true infrastructure. While you may think ‘that’s the command-and-control server,’ actually it’s not. It’s just an intermediary between the proxy servers and the real command-and-control or exploit server.”

“Behind the scenes, the criminals have to prepare for robustness, redundancy and scale…much like the good guys do,” Hubbard adds. “If they don’t, they will be taken down, taken over and be ineffective. The smarter attackers end up building these very robust transient networks where one piece can go down and the rest keeps running.”

Cross-team Collaboration

“Within 10 days of the Cisco acquisition, we were sharing data with the Talos team,” Hubbard added. “We were exchanging data and research on TeslaCrypt and Angler, which helps paint a picture of the operators’ infrastructure.” He added that OpenDNS Security Labs and Talos experts have collaborated before on other projects, due to their shared research interests.

That research, and the data on Angler collected by both OpenDNS and Talos is as broad as it is deep. Starting in June 2013 at BSides Raleigh, OpenDNS Research Labs’ Dhia Mahjoub first described Angler’s use of the “domain shadowing” technique to evade detection by network security products. This behavior was later also described by Talos researchers Nick Biasini and Joel Esler in an in-depth analysis of Angler published in March of this year. Mahjoub further described Angler’s architecture in talks at Virus Bulletin, Black Hat and other conferences during 2014.

Hubbard said that one of the takeaways from this latest takedown is how OpenDNS and Talos researchers can leverage their different, but mutually-reinforcing skills to uncover other ongoing campaigns.

“OpenDNS has developed very accurate models that can predict where attackers behind Angler are going to move next. For example, we can analyze traffic spikes and how these spikes relate to the Angler infrastructure that attackers own versus other online infrastructure,” said Hubbard. “Because we see all of the DNS traffic, we know there are connections in our graph of data that indicate people who are infected with Angler get CryptoWall and also TeslaCrypt. But Talos actually had a hunting team that was able to go in and pull the infrastructure out. This ability, combined with the great sample data Talos has through Threat Grid and AMP can provide real attribution to attacks.”

For more information about Angler, exploit kits and today’s announcement, check out the infographic below. For more detailed information from the Talos team, visit the Cisco Security blog.


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