ESXi / Hyper-V Virtualization Encrypted by Ransomware

Not necessarily. A VM consists of very small configuration files and very large disk payload files, and to finish before detection encryptors often touch only the configuration files and a fraction of each disk. An "invalid" VM in the interface usually means the configuration file was destroyed, not that the disk data is gone. In the publicly documented large-scale ESXi campaigns, the official recovery approach was precisely to rebuild VM metadata from virtual disks the malware had not encrypted. So the first step is not reinstalling — it is freezing the scene, imaging at the storage layer, and grading flat-disk encryption coverage VM by VM.

Several directions are worth checking. Array-side snapshots and replicas: the encryptor runs on top of ESXi and usually has no storage array credentials, so SAN snapshots, replication targets and built-in hyperconverged snapshots may be intact. Off-host and off-site backups: backup copies, tape, offline media. Remnants of deleted snapshots: deletion only releases metadata references, so delta files may still be recoverable while VMFS has not been heavily overwritten. Standbys and other cluster members: physical database standbys and cross-site cluster nodes often survive on a different segment. Inventorying all of these is a standard part of assessment.

Four paths are common. First, unpatched hypervisor service vulnerabilities — there have been large-scale campaigns against old ESXi service flaws. Second, a management interface exposed to the internet or reachable directly from the office network. Third, credential reuse: vCenter sharing administrator accounts with the Windows domain, so a compromised domain controller takes the hypervisor with it. Fourth, lateral movement from backup infrastructure, where public reporting documents ransomware operators exploiting credential-disclosure flaws in backup software to obtain privileged credentials. Our forensics phase draws a specific conclusion from hostd, vmkernel and vCenter event logs plus network records.

The principle is the same; the details are not. Hyper-V runs on Windows Server with guests stored as .vhdx / .avhdx files, so it is more often encrypted incidentally by a Windows encryptor — and when the host is domain-joined, a compromised domain controller takes the whole cluster with it. Recovery must also check the integrity of checkpoint chains (avhdx differencing disks). Proxmox is Linux and KVM based, with disks held as qcow2 files or as LVM / Ceph block devices; in the block-device case file-level techniques do not apply and handling resembles a storage-layer incident. What all three share: the management plane must be isolated, accounts must be decoupled from the domain, and backups must live outside the platform.

No. The guests were force-stopped by the attacker, and their disks may still carry web shells, backdoor services, scheduled tasks and attacker-created accounts; putting them straight online restores the entry point too. The correct approach is to bring recovered VMs up on an isolated segment first, hunt for persistence, verify integrity, patch, reset local and domain credentials, and run database and filesystem consistency checks — then return them to production in priority batches. Confirm the entry point is closed as well; re-encryption on the day of recovery is far from rare.

Strongly advised against. Powering on writes to the datastore — swap files, logs, snapshot metadata — potentially overwriting regions needed for reconstruction, and if the encryptor left components or scheduled tasks behind, booting can trigger a second encryption pass. Failed power-on attempts also leave new metadata changes on VMFS that complicate later recovery. The right way to "try" is on the image: attach the copy in a recovery environment and verify disk readability and filesystem state read-only.