Pierluigi Paganini
June 11, 2016
When the source code of the Carberp Trojan was leaked online, numerous threat actors developed their own variants. This process allowed a significant evolution of the malware that increased its sophistication across the time.
One of its successors recently spotted is the Bolek banking Trojan, a polymorphic threat that targets both 32-bit and 64-bit Windows systems.
The Bolek banking Trojan implements advanced features of banking malware, it is able to steal login credentials, perform web injections, it can grab the screen and execute keylogging functions, and intercept the traffic.
It intercepts traffic in such browsers as Microsoft Internet Explorer, Chrome, Opera, and Mozilla Firefox by intercepting function calls.
“It is designed to perform web injections, intercept traffic, take screenshots, to execute keylogging functions, and to steal login credentials for online banking applications. It can also establish reverse RDP connections (back connect) and launch a local SOCKS5 proxy server and HTTP server in order to perform CMD commands.” reported an analysis published by the Doctor Web firm.
The Bolek banking Trojan inherits a number of features from the Trojan.PWS.Panda (Zeus), it can launch a local SOCKS5 proxy server and HTTP server to perform CMD commands.
The malware abuses svchost.exe or winlogon.exe processes to perform its activities.
The Bolek banking trojan borrowed the presence of a virtual file system from Carberp, meanwhile, it uses an evolution of the JUPITER web injection mechanism implemented in the Zeus Trojan. The malware uses JSON for data sharing.
The malware communicates with the C&C server over HTTP POST requests encrypted with AES CBC 128. All transmitted data is encrypted with a special algorithm and is then compressed using the zlib library.
According to the experts from the Phishme security firm, every time the malware infects a PC it creates a randomly-named file folder in the Windows System32 directory and places the following files in it:
“The .exe executable is actually a copy of a Windows system application pulled from C:\windows\system32 directory and moved to this random directory. The .dll is one imported by the first .exe file at runtime and retains its original file name when copied from System32. This pairing of legitimate executable and its imported .dll provides the underpinning for this malware’s novel persistence capabilities. The malware relies on the “known good” nature of these executables to evade detection. In fact, many of the executables selected and copied by this malware are identified in VirusTotal as benign and listed as “safe software”. So everything is good to go and we can move on, right?” reports the analysis published by Phishme.
Another interesting feature implemented by the Bolek banking trojan is its ability to self-propagate from machine to another with a worm-like mechanism.
The malware could be also updated by operators, allowing the to customize its behavior according to their needs.
The sample of malware detected in the wild mainly targeted Russian banks, but it was also spotted in attacks against Poland users.
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(Security Affairs – Bolek banking Trojan, Carberp Trojan)
