Crooks are always creating new ways to improve the malware they use to target bank accounts, and now Brazilian bad guys have made an important addition to their arsenal: the use of PowerShell. Brazil is the most infected country worldwide when it comes to banking Trojans, according to our Q1 2016 report, and the quality of the malware is evolving dramatically. We found Trojan-Proxy.PowerShell.Agent.a in the wild a few days ago, marking a new achievement by Brazil’s cybercriminals.
The malware is distributed using a malicious email campaign disguised as a receipt from a mobile operator with a malicious .PIF file. After the file is executed it changes the proxy configuration in Internet Explorer to a malicious proxy server that redirects connections to phishing pages for Brazilian banks. It’s the same technique used by malicious PACs that we described in 2013, but this time no PACs are used; the changes in the system are made using a PowerShell script. As Windows 7 and newer OS versions are now the most popular in Brazil, the malware will not face a problem running on victims’ computers.
The malware has no C&C communication. After execution it spawned the process “powershell.exe” with the command line “-ExecutionPolicy Bypass -File %TEMP%\599D.tmp\599E.ps1” aiming to bypass PowerShell execution policies. The .ps1 file in the temp folder uses random names. It’s a base64 encoded script capable of making changes in the system.
After some deobfuscation we can see the goal of the script: to change the Internet Settings key and enable a proxy server on it:
And this is the result in the browser of the victim – a small change in the proxy settings:
This change will not only affect IE but all other browsers installed in the system as well, as they tend to use the same proxy configuration set on IE. The proxy domains used in the attack are listed below. All of them use dynamic DNS services and their goal is to redirect all traffic to a server located in the Netherlands (188.8.131.52), where there are several phishing pages for Brazilian banks:
The malware also has other features of interest: it checks for the language of the OS and aborts if it’s not PTBR, a clever trick to avoid infecting Windows versions in languages other than Brazilian Portuguese.
To protect a network against malware that uses PowerShell, it is important to modify its execution, using administrative templates that only allow signed scripts. We are sure this is the first of many that Brazil’s bad guys will code.
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