CVE-2026-0714

Executive Summary

CVE-2026-0714 is a physical attack vulnerability affecting Moxa industrial computers running Moxa Industrial Linux 3 with TPM-backed LUKS full-disk encryption. The vulnerability arises because the discrete TPM module communicates with the CPU over an SPI bus, which is physically exposed on the device's circuit board. An attacker with invasive physical access—requiring device disassembly and attachment of probing equipment to the SPI bus—can capture TPM communications during the boot process. This captured data may then be used offline to decrypt the eMMC storage contents, bypassing the intended disk encryption protections.

The attack is not remotely exploitable and requires extended physical possession, specialized hardware (e.g., logic analyzers, oscilloscopes), and sufficient time for signal capture and analysis. The CVSS score is 0.0 due to the extremely high physical access requirements, but the technical impact is severe for scenarios where device theft or unauthorized physical access occurs.

Supply Chain & Package Security

This vulnerability is not related to software supply chain or package security; it is a hardware-level physical attack vector. No NPM, PyPI, Go, or Ruby packages are involved.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Physical (P) – Requires physical access to the device.
• Attack Complexity (AC): High (H) – Requires specialized equipment, device disassembly, and signal analysis.
• Privileges Required (PR): None (N) – No prior authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The attack affects only the compromised device.
• Confidentiality (C): High (H) – Full decryption of eMMC contents possible.
• Integrity (I): None (N) – No data modification.
• Availability (A): None (N) – No denial of service.

CVSS Score: 0.0 (Base) – The score is 0.0 because the CVSS v3.1 calculator does not assign a score for Physical attack vectors with High complexity and no impact on integrity or availability. However, the confidentiality impact is High, making this a critical concern for physical security.

Threat Level: Medium (due to high physical access requirements, but severe impact if exploited).

Deep Dive & Mechanics

The vulnerability exploits the physical separation between the discrete TPM chip and the CPU in certain Moxa industrial computers. The TPM is connected via an SPI (Serial Peripheral Interface) bus, which is a synchronous serial communication interface used for short-distance communication. During the boot process, the TPM and CPU exchange cryptographic keys and authentication data over this bus to unlock the LUKS-encrypted eMMC storage.

Attack Steps:

1. Physical Access: The attacker must gain physical possession of the device and open the enclosure.
2. SPI Bus Probing: Using a logic analyzer, oscilloscope, or custom probing hardware, the attacker connects to the SPI bus lines (MISO, MOSI, SCLK, CS) on the circuit board.
3. Signal Capture: The attacker captures the TPM communication during a legitimate boot sequence (e.g., when the device is powered on or rebooted).
4. Offline Analysis: The captured SPI traffic is analyzed to extract the TPM-generated keys or authentication tokens.
5. Decryption: Using the extracted keys, the attacker can decrypt the LUKS-encrypted eMMC contents offline, gaining access to all stored data.

Why It Works: The TPM is designed to be tamper-resistant, but the SPI bus traffic is not encrypted or authenticated between the TPM and CPU. An attacker with physical access to the bus can eavesdrop on the communication.

Vulnerable vs. Patched Code

This is a hardware-level vulnerability; there is no software code to compare. The "vulnerable" configuration is any Moxa Industrial Linux 3 device using a discrete TPM connected via SPI for LUKS full-disk encryption. A "patched" configuration would require hardware redesign (e.g., using an integrated TPM, encrypting SPI traffic, or implementing bus obfuscation). No software patch is available.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Physical access to the target Moxa device.
• Device disassembly tools (screwdrivers, spudgers).
• Logic analyzer (e.g., Saleae Logic Pro) or oscilloscope with SPI decoding capability.
• Probing wires or test clips for SPI bus lines.
• Computer with SPI analysis software (e.g., PulseView, Saleae Logic software).
• LUKS decryption tools (e.g., cryptsetup, luksDump).

Lab Setup Steps:

1. Identify SPI Pins: Locate the TPM chip on the PCB. Identify the SPI pins: MISO, MOSI, SCLK, CS (chip select). Refer to the TPM datasheet (e.g., Infineon SLB9670) for pinout.
2. Connect Logic Analyzer: Attach probing wires to the SPI pins. Connect the logic analyzer ground to the device ground.
3. Capture Boot Sequence: Power on the device. Capture the SPI traffic during the boot process (typically a few seconds). Save the capture as a CSV or binary file.
4. Analyze SPI Traffic: Use the logic analyzer software to decode SPI frames. Look for TPM commands (e.g., TPM2_Startup, TPM2_Unseal) and responses containing key material.
5. Extract Keys: Identify the key blob or authentication data. This may require reverse-engineering the TPM command structure.
6. Decrypt eMMC: Use cryptsetup luksOpen with the extracted key to unlock the encrypted partition.

Example SPI Capture (Conceptual):

# Pseudocode for SPI analysis
import spidev
# Not actual exploit code; conceptual only
captured_data = read_spi_capture("boot_traffic.csv")
key = extract_tpm_key(captured_data)
decrypt_luks(key, "/dev/mmcblk0p2")

Blue Team (Defensive)

Detection & Prevention:

• Physical Security: Enforce strict physical access controls (locked cabinets, tamper-evident seals, CCTV monitoring).
• Bus Obfuscation: Implement SPI bus encryption or use TPMs with encrypted communication (e.g., TPM 2.0 with secure channel).
• Tamper Detection: Add tamper sensors that wipe keys or trigger alarms if the device enclosure is opened.
• Boot Integrity: Use measured boot (TPM PCRs) to detect unauthorized boot sequences.
• Audit Logs: Monitor for unexpected device reboots or physical access events.

Honeypot Strategy: Deploy decoy Moxa devices with fake encryption keys to detect physical probing attempts.

Indicators of Compromise (IOCs)

• Physical IOCs:
  • Signs of device tampering (scratches, broken seals, loose screws).
  • Unusual probing marks on PCB near TPM or SPI bus.
  • Presence of logic analyzer or oscilloscope probes on device.
• Digital IOCs:
  • Unexpected device reboots (may indicate attacker capturing boot sequence).
  • Unauthorized access to eMMC partitions (check dmesg for unusual block device access).
  • TPM communication anomalies (e.g., repeated TPM2_Startup commands).

Detection Engineering

YARA Rule

rule CVE_2026_0714_TPM_SPI_CAPTURE {
    meta:
        description = "Detects SPI capture files containing TPM communication patterns"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "CVE-2026-0714"
    strings:
        $tpm_startup = { 80 01 00 00 00 00 00 00 }  // TPM2_Startup command
        $tpm_unseal = { 80 02 00 00 00 00 00 00 }   // TPM2_Unseal command
        $spi_header = { FF FF FF FF }                // Common SPI frame header
    condition:
        any of ($tpm_startup, $tpm_unseal) and $spi_header
}

Sigma Rule

title: Physical TPM SPI Bus Capture Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects physical access attempts to capture TPM SPI bus traffic on Moxa devices
author: Valters IT
date: 2026-01-01
logsource:
    product: linux
    service: kernel
detection:
    selection:
        - EventID: 7  # Kernel module load
          Image: /lib/modules/*/kernel/drivers/spi/spidev.ko
        - EventID: 13  # USB device insertion (logic analyzer)
          DeviceDescription: '*Saleae*' or '*Logic*'
    condition: selection
falsepositives:
    - Legitimate debugging by authorized personnel
level: high

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2026-0714 TPM SPI Capture - Logic Analyzer Network Activity"; flow:to_server; content:"Saleae"; nocase; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Physical Hardening: Place devices in locked enclosures with tamper-evident seals.
2. Access Control: Restrict physical access to authorized personnel only.
3. Monitoring: Implement CCTV and intrusion detection for device locations.

Long-Term Fixes:

• Hardware Redesign: Use TPMs with encrypted SPI communication (e.g., TPM 2.0 with secure channel).
• Integrated TPM: Switch to firmware-based TPM (fTPM) integrated into the CPU, eliminating the external SPI bus.
• Bus Encryption: Implement SPI bus encryption between TPM and CPU (requires hardware support).
• Key Protection: Use TPM sealing with PCR values to bind keys to specific boot configurations.

Vendor Communication: Contact Moxa for official guidance. As of this report, no patch is available.

Valters IT