Super secretive malware wipes hard drive to prevent analysis

Researchers have uncovered new malware that takes extraordinary measures to evade detection and analysis, including deleting all hard drive data and rendering a computer inoperable.

Rombertik, as the malware has been dubbed by researchers from Cisco Systems' Talos Group, is a complex piece of software that indiscriminately collects everything a user does on the Web, presumably to obtain login credentials and other sensitive data. It gets installed when people click on attachments included in malicious e-mails. Talos researchers reverse engineered the software and found that behind the scenes Rombertik takes a variety of steps to evade analysis. It contains multiple levels of obfuscation and anti-analysis functions that make it hard for outsiders to peer into its inner workings. And in cases that main yfoye.exe component detects the malware is under the microscope of a security researcher or rival malware writer, Rombertik will self-destruct, taking along with it the contents of a victim's hard drive.

In a blog post published Monday, Talos researchers Ben Baker and Alex Chiu wrote:

Once the unpacked version of Rombertik within the second copy of yfoye.exe begins executing, one last anti-analysis function is run — which turns out to be particularly nasty if the check fails. The function computes a 32-bit hash of a resource in memory, and compares it to the PE Compile Timestamp of the unpacked sample. If the resource or compile time has been altered, the malware acts destructively. It first attempts to overwrite the Master Boot Record (MBR) of PhysicalDisk0, which renders the computer inoperable. If the malware does not have permissions to overwrite the MBR, it will instead destroy all files in the user’s home folder (e.g. C:\Documents and Settings\Administrator\) by encrypting each file with a randomly generated RC4 key. After the MBR is overwritten, or the home folder has been encrypted, the computer is restarted.

The Master Boot Record starts with code that is executed before the Operating System. The overwritten MBR contains code to print out “Carbon crack attempt, failed”, then enters an infinite loop preventing the system from continuing to boot.

The MBR also contains information about the disk partitions. The altered MBR overwrites the bytes for these partitions with Null bytes, making it even more difficult to recover data from the sabotaged hard drive.

Once the computer is restarted, the victim’s computer will be stuck at this screen until the Operating System is reinstalled:

Effectively, Rombertik begins to behave like a wiper malware sample, trashing the user’s computer if it detects it’s being analyzed. While Talos has observed anti-analysis and anti-debugging techniques in malware samples in the past, Rombertik is unique in that it actively attempts to destroy the computer if it detects certain attributes associated with malware analysis.

Rombertik also uses a variety of less destructive ways to keep its inner workings secret. To evade sandbox tools that allow malware to run in a carefully controlled laboratory environment, the malware writes a byte of random data to memory 960 million times. The delay that results can trip up the sandbox tool. The random writing to memory can also thwart analysis tools that attempt to document the precise behaviors of the malware.

"If an analysis tool attempted to log all of the 960 million write instructions, the log would grow to over 100 gigabytes," the Talos researchers explained. "Even if the analysis environment was capable of handling a log that large, it would take over 25 minutes just to write that much data to a typical hard drive. This complicates analysis."