Sophos has released details of a new ransomware written in Python that attackers used to compromise and encrypt virtual machines hosted on an ESXi hypervisor.
“This is one of the fastest ransomware attacks Sophos has ever investigated and it appeared to precision-target the ESXi platform,” said Andrew Brandt, principal researcher at Sophos.
“Python is a coding language not commonly used for ransomware. However, Python is pre-installed on Linux-based systems such as ESXi, and this makes Python-based attacks possible on such systems. ESXi servers represent an attractive target for ransomware threat actors because they can attack multiple virtual machines at once, where each of the virtual machines could be running business-critical applications or services. Attacks on hypervisors can be both fast and highly disruptive. Ransomware operators including DarkSide and REvil have targeted ESXi servers in attacks.”
The investigation revealed that the attack began at 12:30 a.m. on a Sunday, when the ransomware operators broke into a TeamViewer account running on a computer that belonged to a user who also had domain administrator access credentials.
This allowed the attackers to install a secure network communications tool called Bitvise on the machine belonging to the domain administrator, which gave them remote access to the ESXi system, including the virtual disk files used by the virtual machines.
At around 3:40 a.m., the attackers deployed the ransomware and encrypted these virtual hard drives hosted on the ESXi server.