A Closer Look at the Target Malware, Part II

Yesterday’s story about the point-of-sale malware used in the Target attack has prompted a flood of analysis and reporting from antivirus and security vendors about related malware. Buried within those reports are some interesting details that speak to possible actors involved and to the timing and discovery of this breach.

As is the case with many data breaches, the attackers in this attack used a virtual toolbox of crimeware to get the job done. As I noted in a Tweet shortly after filing my story Wednesday, at least one of those malware samples includes the text string “Rescator.” Loyal readers of this blog will probably find this name familiar. That’s because Rescator was the subject of a blog post that I published on Dec. 24, 2013, titled “Who is Selling Cards from Target?“.

In that post, I examined a network of underground cybercrime shops that were selling almost exclusively credit and debit card accounts stolen from Target stores. I showed how those underground stores all traced back to a miscreant who uses the nickname Rescator, and how clues about Rescator’s real-life identity suggested he might be a particular young man in Odessa, Ukraine.

This afternoon, McAfee published a blog post confirming many of the findings in my story yesterday, including that two malware uploaders used in connection with the Target attack contained the Rescator string:

“z:\Projects\Rescator\uploader\Debug\scheck.pdb”.

A private message on cpro[dot]su between Rescator and a member interested in his card shop. Notice the ad for Rescator’s email flood service at the bottom.

Earlier this morning, Seculert posted an analysis that confirmed my reporting that the thieves used a central server within Target to aggregate the data hoovered up by the point-of-sale malware installed at Target. According to Seculert, the attack consisted of two stages.

“First, the malware that infected Target’s checkout counters (PoS) extracted credit numbers and sensitive personal details. Then, after staying undetected for 6 days, the malware started transmitting the stolen data to an external FTP server, using another infected machine within the Target network.”

Seculert continues: “Further analysis of the attack has revealed the following: On December 2, the malware began transmitting payloads of stolen data to a FTP server of what appears to be a hijacked website. These transmissions occurred several times a day over a 2 week period. Also on December 2, the cyber criminals behind the attack used a virtual private server (VPS) located in Russia to download the stolen data from the FTP. They continued to download the data over 2 weeks for a total of 11 GBs of stolen sensitive customer information. While none of this data remains on the FTP server today, analysis of publicly available access logs indicates that Target was the only retailer affected. So far there is no indication of any relationship to the Neiman Marcus attack.”

Target has taken quite a few lumps from critics who say the company waited too long to disclose the breach, and new details about when it may have known something was wrong are likely to fan those flames. As I wrote yesterday, the point-of-sale malware used in Target referenced a domain within Target’s infrastructure called “ttcopscli3acs”. Several sources, including Seculert’s Aviv Raff and Dmitri Alperovitch at CrowdStrike, searched for other files with that unique string within the corpus of malware uploaded to Virustotal.com, a service that employs more than 40 commercial antivirus tools to produce reports about suspicious files submitted by users.

That search turned up numerous related files — including the aforementioned malware uploaders with Rescator’s nickname inside — all dated Dec. 11, 2013. Since this malware is widely thought to have been custom-made specifically for the Target intrusion, it stands to reason that someone within Target (or a security contractor working at the company’s behest) first detected the malware used in the breach on that date, and then submitted it to Virustotal.

Yesterday’s story cited sources saying the malware used in the Target breach was carefully crafted to avoid detection by all antivirus tools on the market. These two virustotal scan results from Jan. 16 (today) show that even to this day not a single antivirus product on the market detects these two malicious files used in the Target attack. Granted, the antivirus tools used at virustotal.com do not include behavioral detection (testing mostly for known threat signatures). I point it out mainly because nobody else has so far.

Incidentally, in malware-writer parlance, the practice of obfuscating malware so that it is no longer detected by commercial antivirus tools is known as making the malware “Fully Un-Detectable,” or “FUD” as most denizens of cybercrime forums call it. This is a somewhat amusing acronym to describe the state of a thing that is often used by security industry marketing people to generate a great deal of real-world FUD, a.k.a. Fear Uncertainty and Doubt.

[Source: KrebsonSecurity]