Stealthy malware 'Poweliks' resides only in system registry

The malware is persistent across system reboots, despite not having any files on disk

A new malware program called Poweliks attempts to evade detection and analysis by running entirely from the system registry without creating files on disk, security researchers warn.

The concept of "fileless" malware that only exists in the system's memory is not new, but such threats are rare because they typically don't survive across system reboots, when the memory is cleared. That's not the case for Poweliks, which takes a rather new approach to achieve persistence while remaining fileless, according to malware researchers from G Data Software.

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When it infects a system, Poweliks creates a startup registry entry that executes the legitimate rundll32.exe Windows file followed by some encoded JavaScript code. This triggers a process similar in concept to a Matryoshka Russian nesting doll, said Paul Rascagnères, senior threat researcher at G Data, in a blog post.

The JavaScript code checks whether Windows PowerShell, a command-line shell and scripting environment, is present on the system. If it isn't, it downloads and installs it and then it decodes some more code that is actually a PowerShell script.

The PowerShell script is executed by using a trick to bypass a default protection in Windows that prevents the launch of unknown PowerShell scripts without user confirmation, Rascagnères said. The script then decodes and executes shellcode which injects a DLL (dynamic link library) directly into the system memory.

Once it is running in memory, the rogue DLL component connects to two IP (Internet Protocol) addresses in Kazakhstan to receive commands. It can be used to download and install other threats, depending on the attacker's needs and intentions.

During the entire process, from executing the JavaScript code to the final DLL injection, the malware does not create any malicious files on the hard disk drive, making it difficult for antivirus programs to detect it.

Furthermore, the name of the startup registry key created by Poweliks is a non-ASCII character. This is a trick that prevents regedit -- the Windows registry editor tool -- and possibly other programs from displaying the rogue start-up entry, making it difficult for both users and malware analysts to manually spot the infection.

Some Poweliks variants have been distributed through malicious Microsoft Word documents attached to spam emails that purported to come from Canada Post or USPS. The malicious documents exploited a remote code execution vulnerability in Microsoft Office 2003, 2007 and 2010 that was patched by Microsoft in April 2012. However, according to other reports, the malware is also distributed through drive-by download attacks that use Web exploits.

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To block malware like Poweliks, "antivirus solutions have to either catch the file (the initial Word document) before it is executed (if there is one), preferably before it reached the customer's email inbox," Rascagnères said. "Or, as a next line of defense, they need to detect the software exploit after the file's execution, or, as a last step, in-registry surveillance has to detect unusual behavior, block the corresponding processes and alert the user."

Security researchers from Trend Micro, who have also analyzed the threat, believe that other malware creators may adopt the techniques used by Poweliks in the future.

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