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7.3 Ensure that 'Unattached disks' are encrypted with 'Customer Managed Key' (CMK) (Automated)​

Profile Applicability​

• Level 2

Description​

Ensure that unattached disks in a subscription are encrypted with a Customer Managed Key (CMK).

Rationale​

Managed disks are encrypted by default with Platform-managed keys. Using Customer-managed keys may provide an additional level of security or meet an organization's regulatory requirements. Encrypting managed disks ensures that its entire content is fully unrecoverable without a key and thus protects the volume from unwarranted reads. Even if the disk is not attached to any of the VMs, there is always a risk where a compromised user account with administrative access to VM service can mount/attach these data disks, which may lead to sensitive information disclosure and tampering.

Impact​

NOTE: You must have your key vault set up to utilize this. Encryption is available only on Standard tier VMs. This might cost you more.

Utilizing and maintaining Customer-managed keys will require additional work to create, protect, and rotate keys.

Audit​

From Azure Console​

  1. Go to Disks
  2. Click on Add Filter
  3. In the filter field select Disk state
  4. In the Value field select Unattached
  5. Click Apply
  6. for each disk listed ensure that Encryption type in the encryption blade is `Encryption at-rest with a customer-managed key'

From Azure Command Line Interface 2.0

Ensure command below does not return any output.

az disk list --query '[? diskstate == `Unattached`].{encryptionSettings: encryptionSettings, name: name}' -o json

Sample Output:

[
 {
 "encryptionSettings": null,
 "name": "<Disk1>"
 },
 {
 "encryptionSettings": null,
 "name": "<Disk2>"
 }
]

Remediation​

If data stored in the disk is no longer useful, refer to Azure documentation to delete unattached data disks at:

-https://docs.microsoft.com/en-us/rest/api/compute/disks/delete
-https://docs.microsoft.com/en-us/cli/azure/disk?view=azure-cli-latest#az-disk-delete

If data stored in the disk is important, To encrypt the disk refer azure documentation at:

-https://docs.microsoft.com/en-us/azure/virtual-machines/disks-enable-customer-managed-keys-portal
-https://docs.microsoft.com/en-us/rest/api/compute/disks/update#encryptionsettings

References​

https://docs.microsoft.com/en-us/azure/security/fundamentals/azure-disk-encryption-vms-vmss
https://docs.microsoft.com/en-us/azure/security-center/security-center-disk-encryption?toc=%2fazure%2fsecurity%2ftoc.json
https://docs.microsoft.com/en-us/rest/api/compute/disks/delete
https://docs.microsoft.com/en-us/cli/azure/disk?view=azure-cli-latest#az-disk-delete
https://docs.microsoft.com/en-us/rest/api/compute/disks/update#encryptionsettings
https://docs.microsoft.com/en-us/cli/azure/disk?view=azure-cli-latest#az-disk-update
https://docs.microsoft.com/en-us/security/benchmark/azure/security-controls-v3-data-protection#dp-5-encrypt-sensitive-data-at-rest