On a supported Windows PC, Kernel DMA Protection helps prevent external Thunderbolt and other PCIe devices from reading or changing memory while the computer is locked. Check its status under Windows Security > Device security > Core isolation details > Memory access protection. Protection during boot is a separate matter: Windows’ status does not confirm that the PC’s firmware protects the system before Windows loads.
How a Thunderbolt connection can threaten a locked PC
Thunderbolt and other hot-plug interfaces that use PCI Express can connect devices capable of direct memory access (DMA). DMA lets a peripheral access system memory without the usual CPU-mediated reads and writes. Microsoft describes “drive-by DMA attacks” as attempts made while the computer’s owner is away, using hardware and software that may be readily available. A locked screen alone is not a complete defense against every such device.
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Kernel DMA Protection uses the system’s input/output memory management unit (IOMMU) to restrict external DMA. What happens to a connected device depends partly on whether its driver supports DMA remapping:
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- Compatible driver: Windows can start the device while restricting its DMA to assigned memory regions. A compatible device may therefore continue to work while the screen is locked.
- Incompatible driver: By default, Windows blocks the device from starting until an authorized user signs in or unlocks the screen, subject to the system’s external-device enumeration policy.
That default has a practical boundary: if an incompatible device was started after the PC was unlocked, it can keep working when the screen is locked again, until the device is unplugged or the PC reboots. Administrators can also change external-device enumeration behavior through Group Policy or mobile device management. See Microsoft’s Kernel DMA Protection documentation and its guidance on enabling DMA remapping for device drivers.
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Check whether Kernel DMA Protection is active
- Open Windows Security.
- Select Device security.
- Open Core isolation details.
- Find Memory access protection. Microsoft Support explains this setting in its Device Security in the Windows Security app guidance.
You can also open System Information by running msinfo32.exe, then check the System Summary entry labeled Kernel DMA Protection. ON means the feature is active. Supported systems enable Kernel DMA Protection automatically; seeing the setting on one PC does not mean every PC supports it.
If the setting is off, check firmware support
Kernel DMA Protection requires UEFI firmware support. Microsoft says Virtualization-based Security (VBS) is not required. In System Information, check Hyper-V – Virtualization Enabled in Firmware. If it shows NO on an applicable Intel system, Microsoft advises enabling Intel Virtualization Technology and Intel VT-d in UEFI settings, then returning to Windows and checking Kernel DMA Protection again.
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UEFI menus and option names vary by PC maker, so use the manufacturer’s instructions rather than assuming there is one universal BIOS path. If the feature remains off after checking relevant firmware settings, Microsoft says the system may not support it. Do not treat an absent or inactive setting as proof that the machine is protected.
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Windows’ protection does not establish protection during boot
Kernel DMA Protection covers Windows runtime behavior, not every stage of startup. Microsoft Learn states that the feature “doesn’t protect against drive-by DMA attacks during Boot” and assigns responsibility for Thunderbolt protection during boot to the system firmware/BIOS. An ON status in Windows therefore does not by itself confirm what happens before Windows loads.
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If you need assurance about this boot-time interval, consult the PC manufacturer’s firmware documentation or your organization’s IT administrator. The relevant protection must come from the platform firmware, not merely from the Windows setting.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What to take from the status check
- Memory access protection is on: Windows Kernel DMA Protection is active, but firmware protection during boot remains a separate question.
- It is off and firmware virtualization is disabled: Check the PC maker’s UEFI guidance; on applicable Intel systems, Microsoft identifies Intel Virtualization Technology and VT-d as relevant settings.
- It remains off after the firmware check: The PC may not support Kernel DMA Protection. Ask the manufacturer or IT administrator about the platform’s capabilities and firmware protections.
Microsoft also notes that Kernel DMA Protection is incompatible with older BitLocker DMA-attack countermeasures and recommends disabling those countermeasures if a system supports Kernel DMA Protection. That is platform guidance, not a reason to change BitLocker settings casually; device configuration and organizational policy may differ.
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