December 17, 2013

Exploit Kits "Lacking P(a)unch"

Ran Mosessco Principal Security Researcher

Criminal groups formerly using the Blackhole exploit kit experiment with the Magnitude exploit kit, social engineering techniques, direct attachments, phishing, and fraud


Over the past two months, the criminal gangs that were using malicious email redirecting to the BlackHole exploit kit have made major changes to their tactics, techniques, and procedures, providing some interesting insights into the financially motivated cyber criminal community.  While there has been a considerable amount of discussion about "what is the next big exploit kit?," after the arrest of Blackhole creator Paunch, data from the Websense® ThreatSeeker® Intelligence Cloud (described in detail below) shows that a major criminal group is trending away from Blackhole, and instead experimenting with the up-and-coming Magnitude exploit kit, but not at the volume and frequency we have come to expect from them. In addition, we have observed another major group using Cutwail that appears to have shifted from originally using Blackhole to deliver Pony and ZeuS GameOver malware to focusing increasingly on direct attachments for delivery.

Below is a timeline describing email-based attack trends that we have observed during the recent decline of Blackhole

  • Late September 2013 had a typical mix of attachment and non-attachment spam on the Cutwail botnet with heavy usage of the Blackhole exploit kit to deliver malware.
  • October 4-9 - news broke of the arrest of Blackhole creator Paunch.
  • October 16-18, November 12 - we saw malicious email with the same type of redirection code that had been leading to the Blackhole exploit kit redirecting to the up-and-coming Magnitude exploit kit ("/news/" or "ru:8080" gang).
  • On October 1, October 28, December 4, 5 - we saw URL structures that formerly redirected to Blackhole lead to "American Express themed" phishing pages (3 .js URLs in each page, a URL structure used by the "/topic/" or "Pony/ZeuS GameOver" gang).
  • On December 11-13 - we noticed a shift in URLs formerly used by the "/closest/" gang to connect to Blackhole leading to fraudulent "work from home" and "diet" pages.  


One of the most prolific botnets in existence, Cutwail, at one time had the capacity to produce up to 46% of global spam (according to research reports). Cutwail is commonly used by criminal groups to distribute spam targeting the financial industry via malware capable of stealing banking credentials and credit card numbers. Historically, malicious email sent from the Cutwail botnet has contained a mixture of URLs and ZIP attachments with executables.The intent of Cutwail campaigns is typically to focus on stealing banking credentials and credit card numbers, the email typically impersonate popular banks and financial institutions, major social networks, news organizations, and online retail sites.  URL links contained in these email have typically redirected to the Blackhole exploit kit, which deliver downloaders for malware (with ZeuS GameOver variants being the majority). A second approach uses malicious ZIP attachments in Cutwail email that contains executables that eventually download ZeuS GameOver variants. However, this approach is not as technically sophisticated as the previous technique of a URL leading to the Blackhole exploit kit that does not require a user to "double-click" an executable to infect their computer. 

In early October 2013, Paunch, the proprietor of the infamous Black Hole exploit kit, was arrested by Russian authorities which affected the business model of a few cyber criminal gangs. In the wake of Paunch's arrest, there has been quite a bit of discussion about the future of Blackhole and competitive exploit kits. Security researcher Kafeine has a detailed analysis of the different gangs that were using Black Hole and their activities before and after the arrest.

A shift in tactics

According to Websense telemetry, it appears that since Paunch's arrest in October 2013, the focus of large-scale malicious email campaigns sent via Cutwail has shifted to using attachments, with a short fling using the up-and-coming Magnitude exploit kit seen in October and November (/news/ gang), phishing campaign in December (/topic/ gang).

SPAM Traffic

The data above is generated from one of the Websense real-time analytics that detects Cutwail spam bot campaigns. The analytic operates both in our honeypot and production environments, and outputs both the total number of email that it detects (containing both malicious links and ZIP attachments), and the subset of email containing attachments (ZIP mostly). While this particular real-time analytic captures only a sample of the Cutwail SPAM that we block, the breakdown of SPAM email with attachments with our real-time analytics to detect exploit kits illustrates a clear trend, initially moving away from Blackhole after Paunch's arrest, experimenting with Magnitude but at lower volume than before, and then moving almost entirely to direct email attachments. It is important to remember that more than one criminal group is using Cutwail. We differentiate gangs based on their malware delivery techniques and targets.


Why the shift?

It is important to remember that cyber criminals are financially motivated. The business arrangements between the criminal gangs and Paunch were lucrative, and it may be the case that Magnitude's business model or effectiveness (most likely measured by infection rate) did not justify the cost for the gang  ("/news/" or "ru:8080 gang") that experimented with it, to go full bore as we have seen in their earlier campaigns. Another surprising conclusion could be that the "/topic/" or "Zeus GameOver" gang have seen that direct attachments to email are still effective, and they have decided to invest their resources in other areas.

Similarly, use of existing attack infrastructure for redirection to phishing pages or to less sophisticated malware download sites can be the criminals' way of experimenting with new techniques until a good working relationship is established with the people behind one or more of the existing (or upcoming) exploit kits.

Incidentally, we have seen that some of the ZeuS variants that are delivered through attachments, such as the Upatre downlader, continue to download other malware. Given enough time to run on a victim machine, Upatre sometimes downloaded ransomware such as CryptoLocker, which may have been generating increased revenue for criminal gangs, even with lower infection rates after the decline of Blackhole.

What's next?

We predict that in the next months, there will be a return to URL-based email attacks utilizing exploit kits that offer "malware as a service" on a larger scale. The use of exploit kits is simply a more effective delivery mechanism—especially with an increasingly security-aware target audience. 


Ran Mosessco

Principal Security Researcher

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