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Ransomware Campaign Exploits Known VMware Vulnerability

Both France’s and Italy’s Computer Emergency Response Teams (CERTs) have issued alerts warning “of attack campaigns targeting VMware ESXi hypervisors with the aim of deploying ransomware on them.” The vulnerability (CVE-2021-21974) affects ESXi 7.0, 6.7 and 6.5. Support for ESXi 6.7 and 6.5 ended in October 2022. The flaw was disclosed, and a fix was released in February 2021.


  • The exploited vulnerability is two years old. However, patching Hypervisors like VMware can be tricky. It is even more important to harden your hypervisor and to not expose any administrative interfaces.
  • The good news is that there aren’t that many vulnerable targets out there, but that is bad news if you are one of the 300+ running unsupported and/or unpatched old ESXi versions. There have been enough successful fines and lawsuits against companies running unsupportable software that you can use this as an event to brief management on to justify updating.
  • Have you considered when you’re moving to ESXi 8? If you’re still on ESXi 6.x you may want to jump all the way to version 8.0a. If you’re running without vCenter, and procrastinating upgrading, you can boot the installer and replace your ESXi installation while preserving the volumes with your VMs, then import them. Also make sure that the SLP service is disabled if you’re not using it.
  • What is troubling about this ransomware campaign is that it uses a vulnerability for which a patch was made available two years ago. So why are so many targets available to create a campaign around? It boils down to a matter of economics: it costs downtime and money to patch. We are quick to blame the IT staff for, well, incompetence. Perhaps, just perhaps it is also a business decision to not patch and unfortunately outside of their control. Now we get to measure the other part of the economics scale, the cost in recovery and clean-up.


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