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VHDX file infected by ransomware:
symptoms, impact, and recovery

1️⃣ Context

VHDX files are virtual disks used by Hyper-V, often containing full operating systems or critical business data. When a ransomware infects the host system or the VHDX file itself, it can encrypt the entire content of the virtual disk, making all files, applications, and virtual systems inaccessible.

2️⃣ Symptoms of an encrypted VHDX

Typical signs of a compromised VHDX file include:
  1. Inaccessibility of the virtual disk:
    • The file cannot be mounted in Hyper-V.
    • Error message: “The virtual disk is corrupted or unreadable.”
  2. Modification of the file name or extension:
    • Some ransomware strains rename the file or add extensions such as .locked, .anubis, .crypt.
  3. Increase or decrease in file size:
    • After encryption, the size may slightly change due to the encryption process.
  4. Presence of a ransom note:
    • Files such as README.txt or RESTORE_FILES.html appear in the directory containing the VHDX.
  5. Guest system failure:
Even if Hyper-V attempts to mount the disk, internal files remain unreadable or corrupted.

3️⃣ Impact on data recovery

Data recovery from an encrypted VHDX depends on several factors:

3.1 Type of ransomware

  • If the ransomware uses strong asymmetric encryption (AES, RSA, or ECIES), decryption is nearly impossible without the private key.
  • Some ransomware variants include a wiper that overwrites the virtual disk content, making any traditional recovery impossible.

3.2 Integrity of the VHDX file

  • If the VHDX file has been altered or truncated, the virtual disk may become corrupted.
  • Hyper-V will no longer recognize the disk or its partitions.

3.3 Available backups

  • Isolated backups (offline, tape, immutable snapshots) may allow fast recovery.
  • VHDX files stored on a NAS or network server may also have been encrypted if the ransomware had network access.

3.4 Technical complexity

  • VHDX files often contain NTFS or ReFS file systems, which require file system reconstruction before data can be accessed.
  • Standard data recovery tools are generally insufficient.

4️⃣ Time required to recover the data

The recovery time for an encrypted VHDX varies depending on the situation:
Scenario Average time Key factors
Intact VHDX + isolated full backup < 2h Fast deployment, Hyper-V restoration
Encrypted VHDX without wiper + specialized tool 1–5 days VHDX size, encryption complexity, server CPU
Corrupted VHDX + manual file system reconstruction 5–15 days Disk size, fragmentation, VHDX condition
Encrypted VHDX + active wiper Variable, sometimes impossible Data permanently overwritten
Note: Multi-terabyte VHDX files may require several days, even with professional tools, to rebuild the internal structure and recover usable data.

5️⃣ Tools and methods

  1. Restoration from backup
    • Veeam, Hyper-V Backup, Synology Hyper Backup, LTO tapes.
  2. Manual file system reconstruction
    • Specialized software (ScanX, R-Studio, ReclaiMe) for BTRFS, ReFS, NTFS.
  3. Decryption (if a key is available)
    • Rare: depends on the ransomware and the private key.
  4. Selective extraction
In some partially encrypted VHDX files, only certain files may be recoverable.

6️⃣ Best practices after a VHDX ransomware attack

  • Do not attempt to open or repair the VHDX yourself to avoid worsening the corruption.
  • Isolate the VHDX file on secure, offline storage.
  • Consult a specialist in post-ransomware data recovery.
  • Check backups and immutable snapshots before any action.
Document the incident for insurance or post-incident reporting.