Guidance for configuring BitLocker to enforce software encryption

Security Advisory

Released: Nov 6, 2018

Assigning CNA
Microsoft

Executive Summary

Microsoft is aware of reports of vulnerabilities in the hardware encryption of certain self-encrypting drives (SEDs). Customers concerned about this issue should consider using the software only encryption provided by BitLocker Drive Encryption™. On Windows computers with self-encrypting drives, BitLocker Drive Encryption™ manages encryption and will use hardware encryption by default. Administrators who want to force software encryption on computers with self-encrypting drives can accomplish this by deploying a Group Policy to override the default behavior. Windows will consult Group Policy to enforce software encryption only at the time of enabling BitLocker.

To check the type of drive encryption being used (hardware or software):

  1. Run ‘manage-bde.exe -status’ from elevated command prompt.
  2. If none of the drives listed report "Hardware Encryption" for the Encryption Method field, then this device is using software encryption and is not affected by vulnerabilities associated with self-encrypting drive encryption.

For drives that are encrypted using a vulnerable form of hardware encryption, you can mitigate the vulnerability by switching to software encryption using Bitlocker with a Group Policy.

Note: After a drive has been encrypted using hardware encryption, switching to software encryption on that drive will require that the drive be unencrypted first and then re-encrypted using software encryption. If you are using BitLocker Drive Encryption, changing the Group Policy value to enforce software encryption alone is not sufficient to re-encrypt existing data.

IMPORTANT: You do NOT need to reformat the drive or reinstall any applications after changing BitLocker settings.

To mitigate vulnerabilities associated with self-encrypting drives on Windows systems:

  1. Configure and deploy a Group Policy to enable forced software encryption.
  2. Fully turn off BitLocker to decrypt the drive.
  3. Enable BitLocker again.

For more information on Bitlocker and Group Policy settings to enforce software encryption:

Exploitability

The following table provides an exploitability assessment for this vulnerability at the time of original publication.

Publicly disclosed
Yes
Exploited
No
Exploitability assessment

Acknowledgements

Microsoft recognizes the efforts of those in the security community who help us protect customers through coordinated vulnerability disclosure. See Acknowledgements for more information.

Security Updates

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Revisions

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