Level 13
Malware Tester
Antivirus maker Kaspersky said in a report today that hackers associated with the North Korean regime are behind a new ransomware strain known as VHD.
The report details two incidents to which Kaspersky was privy, where intruders gained access to companies' networks and deployed the VHD ransomware.


Level 44
Content Creator
Malware Hunter
The ransomware itself is nothing special: it’s written in C++ and crawls all connected disks to encrypt files and delete any folder called “System Volume Information” (which are linked to Windows’ restore point feature). The program also stops processes that could be locking important files, such as Microsoft Exchange and SQL Server. Files are encrypted with a combination of AES-256 in ECB mode and RSA-2048. In our initial report published at the time we noted two peculiarities with this program’s implementation:
  • The ransomware uses Mersenne Twister as a source of randomness, but unfortunately for the victims the RNG is reseeded every time new data is consumed. Still, this is unorthodox cryptography, as is the decision to use the “electronic codebook” (ECB) mode for the AES algorithm. The combination of ECB and AES is not semantically secure, which means the patterns of the original clear data are preserved upon encryption. This was reiterated by cybersecurity researchers who analyzed Zoom security in April 2020.
  • VHD implements a mechanism to resume operations if the encryption process is interrupted.
Whenever a successful connection was made, a network share was mounted, and the VHD ransomware was copied and executed through WMI calls. This stood out to us as an uncharacteristic technique for cybercrime groups; instead, it reminded us of the APT campaigns Sony SPE, Shamoon and OlympicDestroyer, three previous wipers with worming capabilities.
this attack did not fit the usual modus operandi of known big-game hunting groups. In addition, we were only able to find a very limited number of VHD ransomware samples in our telemetry, and a few public references. This indicated that this ransomware family might not be traded widely on dark market forums, as would usually be the case.
The highlighted/underlined notes is clearly seen on analysis services, but also partial in the sample shared in the Hub :