Researchers Disrupt Angler Exploit Kit, Ransomware Operation

Cisco Talos Group has disrupted the operations and compromised the infrastructure used by the operators of the popular Angler Exploit Kit, "the most effective exploit kit that Talos has seen." Angler is principally delivering the TeslaCrypt and CryptoWall ransomware, and generating approximately $60 million per year on ransomware alone, researchers estimte. 

Talos, collaborating with OpenDNS and Level 3 Threat Research, investigated Angler's telemetry data and found that a large amount of its activity was being generated within a single provider, Limestone Networks. Working with Limestone Networks, the researchers obtained live disk images of Angler servers to watch the campaign in action.

Through July, they observed activity from one exploit server and one health monitoring server, which performed health checks on host machines and remotely erased log files on hosts. They discovered that Angler operators were extensively using proxy servers to hide their infrastructure from investigators -- the one health monitoring server monitored 147 proxies.

Another way Angler has managed to evade security teams is its use of referers. According to the report, researchers found "more than 15,000 unique sites pushing people into the exploit kit, 99.8% percent of which were used less than ten times, illustrating the low frequency. That means that the majority of referers were only active for a short period of time and were removed after a handful of users were targeted. This is one of the features that makes Angler so difficult to hunt."

One primary actor is responsible for 50 percent of Angler's activity, and making over $30 million per year from ransomware alone, according to researchers, who therefore estimate that Angler overall could be generating $60 million from ransomware.

In response to these findings, Cisco contacted affected hosting providers so they could shut down servers, updated its products to stop redirects to Angler proxies (thereby cutting off Anglers' access to Cisco customers), released Snort rules to detect and block checks from health monitoring servers, and published indicators of compromise.