Pre-OS Boot × Microsoft BitLocker

bypass Microsoft BitLocker's default TPM-only encryption

The attack exploits the fact that in TPM-only mode, the plaintext VMK is transmitted over physical wires from the TPM to the CPU during boot. An attacker with physical access removes the laptop's back cover, attaches a logic analyzer or similar low-cost hardware to the TPM bus (e.g., SPI), and captures the VMK as it is sent. With the VMK, the attacker can decrypt the Full Volume Encryption Key (FVEK) from disk metadata and access the encrypted data, or recover the BitLocker recovery passphrase.

Monitor for physical tampering indicators such as chassis intrusion detection logs from endpoint management systems or TPM attestation failures in remote attestation reports. Mitigate by configuring BitLocker with TPM+PIN or TPM+USB key to prevent VMK exposure even if the bus is sniffed, and enforce physical security controls to limit unauthorized access.