TL;DR
Yes, a determined physical attacker can compromise a Windows machine even with UEFI secure boot and BitLocker enabled. While these features significantly raise the bar, they aren’t impenetrable. Attacks like cold boot attacks, firmware attacks (e.g., using tools like Flashrom), and direct memory access (DMA) can bypass these protections. Mitigation involves physical security measures, hardware-based root of trust, and careful configuration.
Understanding the Protections
Let’s quickly recap what UEFI Secure Boot and BitLocker do:
- UEFI Secure Boot: Ensures only trusted operating system loaders (and drivers) can run during startup, preventing malware from hijacking the boot process.
- BitLocker: Full-disk encryption that protects all data on your drive. Requires a password/PIN/TPM to unlock.
How an Attacker Can Bypass Protections
- Cold Boot Attack:
- What it is: Exploits the fact that RAM retains data for a short period after power loss. The attacker quickly reboots into a special environment to dump the encryption key from memory before it’s lost.
- Mitigation: Full system shutdown (not just restart), using TPM-based BitLocker, and enabling hardware-based root of trust can help.
- Firmware Attacks (e.g., Flashrom):
- What it is: The attacker physically accesses the motherboard to reprogram the UEFI firmware with a malicious version. This allows them complete control over the system, bypassing Secure Boot entirely.
- Mitigation: Physically secure the machine (tamper-evident enclosures), use firmware write protection features if available in your BIOS/UEFI settings, and regularly check firmware integrity.
- Direct Memory Access (DMA) Attacks:
- What it is: DMA allows hardware components to directly access system memory without CPU intervention. An attacker can connect a malicious device (e.g., Thunderbolt, FireWire, PCIe card) and read/write memory, potentially extracting BitLocker keys or injecting code.
- Mitigation: Disable unused DMA-capable ports in the BIOS/UEFI settings. Use IOMMU to isolate devices. Consider hardware solutions that prevent unauthorized DMA access (e.g., Thunderbolt security features).
- TPM Bypass (Less Common, More Complex):
- What it is: Attackers can attempt to physically manipulate the TPM chip or exploit vulnerabilities in its firmware. This requires specialized equipment and expertise.
- Mitigation: Use a reputable TPM module from a trusted manufacturer. Regularly update the TPM firmware.
Practical Mitigation Steps
- Physical Security is Paramount: The most effective defense is preventing physical access to the machine. Use locked server rooms, tamper-evident enclosures, and strong security policies.
- Full System Shutdowns: Avoid restarts whenever possible; perform full shutdowns to clear RAM contents.
- TPM Integration: Always use a TPM module with BitLocker. Configure BitLocker to require the TPM for unlocking.
manage-bde -protectors -add C: -tpm - BIOS/UEFI Settings Review:
- Enable Secure Boot (if not already enabled).
- Disable unused ports (e.g., FireWire, Thunderbolt) in the BIOS/UEFI settings.
- Check for and enable firmware write protection features.
- Configure IOMMU if supported by your hardware.
- Firmware Updates: Regularly update your UEFI firmware to patch security vulnerabilities.
- Hardware-Based Root of Trust: Consider using systems with a robust hardware root of trust that provides strong protection against firmware attacks.
Conclusion
UEFI Secure Boot and BitLocker are valuable security features, but they don’t provide complete protection against physical attacks. A layered approach combining physical security measures, careful configuration, and hardware-based root of trust is essential to mitigate the risks.