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.
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.
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.
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.