Article ID: 2516445 - View products that this article applies to.
Support for Windows Vista Service Pack 1 (SP1) ended on July 12, 2011. To continue receiving security updates for Windows, make sure that you're running Windows Vista with Service Pack 2 (SP2). For more information, go to the following Microsoft website: Support is ending for some versions of Windows
A BitLocker-protected computer may be vulnerable to Direct Memory Access (DMA) attacks when the computer is turned on or is in the Standby power state. This includes when the desktop is locked.
BitLocker with TPM-only authentication lets a computer to enter the power-on state without any pre-boot authentication. Therefore, an attacker may be able to perform DMA attacks.
In these configurations, an attacker may be able to search for BitLocker encryption keys in system memory by spoofing the SBP-2 hardware ID by using an attacking device that is plugged into a 1394 port. Alternatively, an active Thunderbolt port also provides access to system memory to perform an attack.
This article applies to the following systems:
1394 physical DMA
Industry standard 1394 controllers (OHCI compliant) provide functionality that allows for access to system memory. This functionality is provided as a performance improvement. It enables large amounts of data to transfer directly between a 1394 device and system memory, bypassing CPU and software. By default, 1394 Physical DMA is disabled in all versions of Windows. The following options are available to enable 1394 Physical DMA:
BitLocker system integrity checks protect against unauthorized Kernel Debugging status changes. However, an attacker could connect an attacking device to a 1394 port, and then spoof an SBP-2 hardware ID. When Windows detects an SBP-2 hardware ID, it loads the SBP-2 driver (sbp2port.sys), and then instructs the driver to allow for the SBP-2 device to perform DMA. This enables an attacker to gain access to system memory and search for BitLocker encryption keys.
Thunderbolt physical DMA
Thunderbolt is a new external bus that has functionality that allows for direct access to system memory. This functionality is provided as a performance improvement. It enables large amounts of data to transfer directly between a Thunderbolt device and system memory, thereby bypassing the CPU and software. Thunderbolt is not supported in any version of Windows, but manufacturers might still decide to include this port type.
Thunderbolt threats to BitLocker
An attacker could connect a special purpose device to a Thunderbolt port and have full direct memory access via the PCI Express bus. This could enable an attacker to gain access to system memory and search for BitLocker encryption keys.
Some configurations of BitLocker can reduce the risk of this kind of attack. The TPM+PIN, TPM+USB, and TPM+PIN+USB protectors reduce the effect of DMA attacks when computers do not use sleep mode (suspend to RAM). If your organization allows for TPM-only protectors or supports computers in sleep mode, we recommend that you block the Windows SBP-2 driver and all Thunderbolt controllers to reduce the risk of DMA attacks.
For more information about how to do this, go to the following Microsoft website:
Step-By-Step Guide to Controlling Device Installation Using Group Policy
SBP-2 MitigationOn the previously mentioned website
(http://technet.microsoft.com/en-us/library/bb530324.aspx), refer to the "Prevent installation of drivers matching these device setup classes" section under "Group Policy Settings for Device Installation".
The following is the Plug and Play device setup class GUID for an SBP-2 drive:
Thunderbolt MitigationImportant The following Thunderbolt mitigation only applies to Windows 8 and to Windows Server 2012. It does not apply to any of the other operating systems that are mentioned in the "Applies to" section.
On the previously mentioned website
(http://technet.microsoft.com/en-us/library/bb530324.aspx), refer to the "Prevent installation of devices that match these device IDs" section under "Group Policy Settings for Device Installation".
The following is the Plug and Play compatible ID for a Thunderbolt controller:
For more information about DMA threats to BitLocker, see the following Microsoft Security blog:
Windows BitLocker ClaimsFor more information about mitigations for cold attacks against BitLocker, see the following Microsoft Integrity Team blog:
Protecting BitLocker from Cold Attacks
Article ID: 2516445 - Last Review: August 8, 2012 - Revision: 3.0