The Return of the Brazilian Banker Trojan

Brazil. It is known as the land of carnivals, beaches, coconuts – and vicious phishing campaigns. These campaigns have long been considered a national threat; on average, a Brazilian organization receives over 1000 phishing attacks per month.

Check Point research team often uses various Brazilian phishing malwares as part of our research training program. In one instance, we gave our trainees a rather old malware, a Trojan commonly known as the “Banker”, which was first spotted in 2009. Banker is not technically complex but serves as a good example for “OSINT”-based research. The results were quite surprising.

Our research shows that while the malware has adapted over the years, the same technique used in the original sample is still very much alive and kicking, and is possibly linked to the same campaign or actor. The latest samples are from January 2016 and the current attack rate detected by Check Point’s ThreatCloud is over 100 attacks per day, only in Brazil.

Overview – how does the malware operate?

The “Banker” malware attempts to steal user credentials in order to make unauthorized money transactions. The infection method is simple and efficient: the malware changes the native operating system proxy configuration. Whenever a user attempts to connect to one of the targeted banks, they are referred to a fake login webpage. Thinking that they are logging into their own bank accounts, the users enter their credentials – which are now in the hands of the attacker.

The proxy configuration files dropped by the malware consist of settings related to specific Brazilian banks and financial institutions. This malware family targets Brazil only, and infected machines spotted outside of the country are most likely the results of lack of distribution planning and inaccuracy.

The chase begins – analyzing the early versions of the malware

Earlier versions of the malware were simple batch files packed by a UPX packer. The malware attempts to change some basic security configurations to remain undetected, such as turning off antivirus and firewall notifications, and disabling browser certificate verification, user account control, and system restore.

In addition, the malware notifies its operators that the specific machine has been successfully infected. It launches a minimized Internet Explorer window and sends the victim’s username and computer name to the C&C at a pre-defined URL whose structure can be seen here:

http://112[.]72.128.242/famas.php?a=%username%-%computername% The malware then copies the proxy configuration to a file in the TEMP folder with the same name as the computer. The configuration file consists of the functions set. These functions are in fact redirections to malicious servers, which are activated when the victim visits one of the listed domains of targeted banks and financial institutions. A sample configuration file, which was obfuscated, contained the names of 23 financial institutions (see Appendix 1).

Following the breadcrumb trails

Further examination of the samples led us to the domain ioffset.info with the following registration address: bbetinha2@gmail.com.

A search for additional domains registered by the same email address revealed the following domain: ixyou.info. After analyzing this domain, we found two connected email addresses: a60a0@play.ixyou.info and root@play.ixyou.info.

We learned that the owner of these new addresses had spread phishing emails containing malicious attachments. We were able to obtain samples of these attachments, and found a number of new domain names and IP addresses. One domain, vks11466.ip-37-59-121.eu, led us to an additional malware sample.

At this point, the trail grew cold, as every possible lead had already been investigated, with no further results.
We conducted additional research on the known indicators-of-compromise. This time, the sample A77219A971029DC2FB683E8513713803 caught our attention.

According to VirusTotal, this sample was not detected by any cyber security vendor, yet during our investigation we already encountered the domain it used:
dll.ixyou.info/xp.txt

And so we were back on track! The domain contained a referral to this filename: xp.txt

The chase continues…

As we turned our focus to collecting samples operating with the filename xp.txt, we were able to get our hands on a Banker sample last spotted on September 28, 2014. This sample is not a batch file, and was compressed with a UPX packer. It was distributed via phishing emails as a flash installer.

A dedicated search led us to another new sample, also undetected according to VirusTotal. This time, the sample was a JAR file – last spotted on December 15th, 2015! Analysis of this sample revealed that the file contains only a single function.

 This function has two actions:

1. Download a proxy configuration file from a URL, and set the local proxy to use this configuration.
2. Open a new Internet Explorer instance and browse to a predefined URL, probably in order to confirm successful infection. The pre-defined URL is: h[tt]p://database.deliveryfaby.com/dadosquantis/

As seen in the commands above, the function and variable names are written in Portuguese. The pre-defined URL is inactive, but all signs lead us to believe that it was indeed used to notify the malware operators of a successful infection.

The sample last spotted on January 27, 2016 is a Java sample whose target list consists of bank names (see Appendix 2).
There are differences between this list and the list of the 2012 batch file targets, but there are many similarities as well. We can also see that the same technique used by the most recent sample is used against customers of the Brazilian financial sector.

Based on these findings, we can determine with high confidence that this sample is indeed related to the original Banker malware – we cannot determine whether the same threat actor is behind all of the various campaigns, but the similarities are clear. This means the Banker Trojan is still actively trying to obtain Brazilian banking credentials, and as seen by samples obtained from different dates, it was probably active all along.

Following this development, we have spotted 782 attacks of the “Banker” malware between 27.1.16-3.2.16, with an average of more than 100 attacks per day.

Conclusion

Despite the commonly held belief that the Banker malware was active primarily in the years 2009 – 2013, the reality is quite different.

Our findings show that the technique used by the original Banker Trojan is still in use, and the malware from the same campaign (or a very similar one) is currently active. This malware presents a current threat to the Brazilian banking system and its users.

Check Point Threat Prevention customers are protected from this threat.