Like the well-known Petya, the Mamba, or HDDCryptor family of ransomware, acts by holding a computer hostage. When it infects a PC, it encrypts data present on the machine as well as the computer’s master boot records, thus rendering the machine unusable.

Mamba was first spotted in the wild in January of this year, making it older than Petya. Security researcher Renato Marinho first noted its resurgence and Trend Micro confirmed his observations.

Mamba Strikes: HDDCryptor in Action

Mamba starts by accessing a malicious website, which it uses as a vector to spread malware. Its files, according to Softpedia, are laced with either HDDCryptor or a different type of malware that delivers the main payload later on. This allows the perpetrators to ensure boot persistence on the infected computer.

Once it infects a PC, the malware scans the local network for network drives. It then uses an open-source password recovery tool to search and exfiltrate the credentials of past and present network-shared folders. This provides DiskCryptor, an open-source disk encryption software, with the information it needs to encrypt network-shared volumes.

DiskCryptor supports AES, Twofish and Serpent encryption algorithms, and their combinations, in XTS mode. It’s a legitimate and capable tool that can be used for criminal purposes.

Finally, HDDCryptor rewrites the infected computer’s master boot record (MBR) with a custom boot loader. It then restarts the computer, at which point a ransom note freezes on the screen.

Forced Reboot

Trend Micro noted that the attack causes the infected system to be “forcefully rebooted” with no user interaction after two hours of full disk activity. Those researchers also observed cases in which an affected machine was rebooted multiple times.

Enterprises should implement preventative measures to deal with ransomware and other threats. These measures may include a strengthened backup policy and a proactive, multilayered approach to security.