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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 virtual files, applications, and systems inaccessible.

2️⃣ Symptoms of an encrypted static or dynamic 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 extension or name:
    • Some ransomware rename the file or add extensions such as .locked, .anubis, .crypt.
  3. Presence of a ransom note:
    • Files such as README.txt or RESTORE_FILES.html in the directory containing the VHDX.
  4. Guest system freeze:
    • Even if Hyper-V attempts to mount the disk, the internal files are unreadable or corrupted.

3️⃣ Impact on data recovery

Data recovery from an encrypted VHDX depends on several factors:

3.1 Type of ransomware

  • Some ransomware include a wiper that overwrites the content of the virtual disk, making any standard recovery impossible.

3.2 Integrity of the VHDX file

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

3.3 Available backups

  • VHDX files stored on a NAS or network server may also have been encrypted if the ransomware accessed the network.

3.4 Technical complexity

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

4️⃣ Tools and methods

  1. Recovery from backup
    • Veeam, Hyper-V Backup, Synology Hyper Backup, LTO tapes.
  2. Manual reconstruction of the file system
  3. Decryption
    • Depends on the ransomware.
  4. Selective extraction

In some partially encrypted VHDX files, only certain files may be recoverable.

5️⃣ Best practices after VHDX ransomware infection

    • 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.