Since the Angler Exploit Kit began in late May spreading Cryptowall 3.0 ransomware, traffic containing the malware has continued to grow, putting more potential victims in harm’s way.

A week ago, the SANS Internet Storm Center reported that Cryptowall 3.0 infections are emanating from not only the prolific exploit kit, but also from malicious spam campaigns. The two means of infections share some common characteristics, lending credence to the theory that the same group may be behind both.
Version 3.0 is the latest iteration of Cryptowall, which is also known as Crowti. Like other ransomware families, Cryptowall 3.0 encrypts files stored on a compromised computer and demands a ransom, usually $500 payable in Bitcoin, in exchange for the encryption key. The malware uses numerous channels to communicate and send stolen traffic to its keepers, including I2P and Tor anonymity networks. Researchers at Cisco in February said that Cryptowall 3.0 abandoned using a dropper for propagation, opting instead to use exploit kits.

As of this morning, SANS incident handler and Rackspace security researcher Brad Duncan said that the latest run of Angler Exploit Kit traffic showed that the attackers had added a different Bitcoin address than the one used previously.

At this point, I’m not 100 percent certain it’s the same actor behind all this Cryptowall 3.0 we’ve been seeing lately,” Duncan wrote on the SANS ISC website. “However, my gut feeling tells me this activity is all related to the same actor or group. The timing is too much of a coincidence.

Duncan said that a check on blockchain.info for activity on the two Bitcoin addresses shows some transactions, indicating some victims are paying the ransom.

“We’re seeing a lot more samples of CryptoWall 3.0 in the spam/EK traffic now than before, so maybe the increased exposure might help infect more computers,” Duncan said, adding that he had no data on whether any of the victims who did pay the ransom were receiving encryption keys and are able to salvage their data.

Duncan said this latest spike began May 25 from both the malicious spam and Angler angles; both campaigns were still active as of early this morning.

The spam campaign uses Yahoo email addresses to send Cryptowall 3.0 via attachments. The attachments are called my_resume.zip and contain an HTML file called my_resume.svg. Duncan said the attackers have begun appending numbers to the file names, such as resume4210.html or resume9647.html.

Opening the attachment and extracting the malicious file gives you an HTML document. If you open one of these HTML files, your browser will generate traffic to a compromised server,” Duncan wrote. “The return traffic is gzip compressed, so you won’t see it in the TCP stream from Wireshark. Exporting the text from Wireshark shows HTML that points to a shared document from a Google server.

Cryptowall is hosted on a number of different docs.google.com URLs, he said, a list of which is posted on the SANS website. The Bitcoin address used for payment in the spam campaign is 16REtGSobiQZoprFnXZBR2mSWvRyUSJ3ag, the same address found in other spam samples.

Infections coming from Angler began May 26, and were the first Cryptowall 3.0 infections seen from Angler. The Bitcoin address used in Angler infections is 16Z6sidfLrfNoxJNu4qM5zhRttJEUD3XoB, SANS said. Duncan reports that a second Bitcoin address, 12LE1yNak3ZuNTLa95KYR2CQSKb6rZnELb, was used as of today.

“There are any number of reasons to use more than one Bitcoin address. It could be a back-up, in case law enforcement is closing in on the other one. It could be a way to track different infections, geographically,” Duncan said. “I’m not sure on this one. It’s just my gut feeling, which could be wrong.”

Duncan said that a new slate of WordPress sites were redirecting to Angler in this campaign, based on web injects observed.

“The significance is that there are plenty of vulnerable websites running outdated or unpatched versions of WordPress,” Duncan said. “The actors behind this (and other) campaigns will have a continuous supply of websites that can be compromised and used for these efforts.”

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