A security researcher has disclosed a boot-chain weakness in HP ThinPro 8 and 9 that could allow attackers with physical access to a thin client to extract its LUKS disk-encryption key.

The issue affects HP thin clients in which LUKS2 protects the operating system’s encrypted root partition, and the decryption key is sealed inside the device’s Trusted Platform Module (TPM).

While this design is intended to prevent data theft from removed storage drives, the researcher found that the TPM policy does not fully validate the software loaded during Boot.

HP ThinPro uses a custom utility, called hptc-tpm-tool, to retrieve the LUKS key from the TPM during startup. An initramfs script named unseal_key requests the key and passes it directly to cryptsetup, which unlocks the encrypted root partition.

HP ThinPro TPM Disk Encryption Flaw

However, the TPM key is reportedly sealed only to PCR 0, PCR 2, and PCR 4. These registers measure BIOS firmware, option ROMs or UEFI drivers, and the GRUB bootloader binary.

They do not measure GRUB configuration commands, the Linux kernel, or the initramfs that GRUB loads. This creates a significant gap.

An attacker cannot simply replace the GRUB binary without changing PCR 4 and blocking key release. But they can modify the unencrypted initramfs, including the shell script that unseals the key, without altering the PCR values the TPM checks.

According to the AmberWolf disclosure, a modified initramfs can copy the recovered LUKS key to the unencrypted BOOT partition before normal startup continues.

On the next Boot, the TPM treats the system as trusted because the firmware and GRUB measurements remain unchanged. The device then starts normally, while the attacker can later retrieve the exposed key from the drive.

The attack requires local physical access and the ability to remove or modify the M.2 SATA storage device. No soldering, specialized hardware, or advanced reverse engineering is required.

The researcher confirmed the issue on an HP t530 running ThinPro 8.1.0 build 22 and an HP t540 running ThinPro 9.0.0 build 15.

Once an attacker obtains the raw 32-byte LUKS key, they can decrypt the protected partition and access device configuration data, certificate stores, stored credentials, and password hashes.

This could have serious consequences for organizations that return, lose, resell, or dispose of thin clients without securely destroying the internal drive.

The flaw was assigned a CVSS 3.1 score of 6.1, rated Medium, based on physical access, low attack complexity, and high impact on confidentiality and integrity.

Secure Boot is turned off by default on affected systems, according to the researcher, although enabling it and setting a BIOS password may only slow down an attacker rather than close the underlying PCR measurement gap.

The researcher reported the issue to HP PSIRT on February 22, 2026. HP reportedly confirmed that a fix was undergoing quality assurance. However, no security bulletin, CVE, or shipped patch was available at the time of disclosure.

Organizations using ThinPro full-disk encryption should treat devices outside their physical control as potentially exposed until HP releases a complete remediation.

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