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threat-modeling.md

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Threat Model Analysis for nodemcu/nodemcu-firmware

Threat: Exploitation of Weak Default Credentials

  • Description: An attacker scans for NodeMCU devices with default Wi-Fi credentials (SSID and password) configured by the firmware itself. The attacker uses these default credentials to gain unauthorized access to the device. This focuses on the firmware's default settings, not those set by a user's Lua script.
  • Impact: Complete device compromise. The attacker can reconfigure the device, upload malicious firmware, steal data, or use the device as part of a botnet.
  • Affected Component: wifi module (specifically, the default configuration provided by the NodeMCU firmware build).
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Firmware Build Configuration: Ensure the firmware build does not include default Wi-Fi credentials. If defaults are absolutely necessary for initial flashing, they must be randomized per-device during the build process and must be changed before network connectivity is enabled. This is a responsibility of the firmware builder/developer, not just the end-user.
    • Mandatory First-Boot Configuration: The firmware should force a secure configuration process (e.g., requiring the user to set a strong Wi-Fi password) before allowing any network access.

Threat: Buffer Overflow in Network Stack

  • Description: An attacker sends specially crafted network packets (e.g., oversized TCP or UDP packets, malformed HTTP requests) to the NodeMCU device. These packets exploit a buffer overflow vulnerability in the firmware's network stack, allowing the attacker to overwrite memory and potentially execute arbitrary code.
  • Impact: Arbitrary code execution, leading to complete device compromise. The attacker can gain full control of the device.
  • Affected Component: net module (TCP/UDP sockets), http module (if used for receiving requests), underlying LwIP network stack (C code within the NodeMCU firmware).
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Firmware Updates: Keep the NodeMCU firmware up-to-date to benefit from any patches addressing buffer overflow vulnerabilities in the network stack. This is the primary mitigation.
    • Fuzzing (Firmware Development): Firmware developers should use fuzzing techniques to test the network stack and related modules for buffer overflow vulnerabilities.
    • Memory Protection (if available): If the hardware and firmware support it, enable memory protection features (e.g., stack canaries, ASLR) to make exploitation more difficult. This is a firmware-level mitigation.

Threat: Cryptographic Weaknesses in TLS/SSL Communication (Firmware Library)

  • Description: An attacker performs a man-in-the-middle (MITM) attack on the NodeMCU device's TLS/SSL communication due to vulnerabilities within the firmware's TLS/SSL library itself (e.g., mbed TLS or BearSSL). This could be due to outdated or vulnerable cryptographic algorithms hardcoded in the library, or flaws in the library's implementation.
  • Impact: Data leakage (e.g., credentials, sensor readings), data manipulation, loss of confidentiality and integrity.
  • Affected Component: Underlying mbed TLS or BearSSL library (C code within the NodeMCU firmware), tls module (as the interface to the library).
  • Risk Severity: High
  • Mitigation Strategies:
    • Firmware Updates: This is the primary mitigation. Keep the firmware up-to-date to benefit from security patches in the TLS/SSL library.
    • Library Selection (Firmware Build): If building the firmware from source, choose a well-maintained and secure TLS/SSL library (e.g., a recent version of mbed TLS or BearSSL).
    • Configuration (Firmware Build): Ensure the TLS/SSL library is configured to use only strong, modern cipher suites by default. Disable support for deprecated or weak ciphers at the firmware build level.

Threat: Insecure Firmware Update (OTA) - Firmware Vulnerability

  • Description: An attacker uploads malicious firmware to the NodeMCU device using the Over-The-Air (OTA) update mechanism. This is possible due to a vulnerability in the firmware's OTA update implementation itself, such as a lack of proper authentication of the new firmware image (e.g., missing or weak digital signature verification).
  • Impact: Complete and persistent device compromise. The attacker gains full control and can replace the legitimate firmware with their own.
  • Affected Component: OTA update mechanism (implementation within the NodeMCU firmware – could be a built-in module or a core firmware component). This is not about a user-written Lua script for OTA, but the underlying firmware support.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Digital Signatures (Firmware Implementation): The firmware must implement robust digital signature verification for firmware images. The device should verify the signature before applying the update. This is a core firmware responsibility.
    • Secure Bootloader (Firmware/Hardware): Use a secure bootloader that verifies the integrity of the firmware at startup. This is a combined firmware and hardware requirement.
    • Rollback Protection (Firmware Implementation): The firmware should implement mechanisms to prevent attackers from downgrading the firmware to a vulnerable version.

Threat: Physical Tampering / Firmware Extraction (Lack of Secure Boot)

  • Description: An attacker with physical access to the device attempts to extract the firmware, modify it, or replace it with malicious firmware. They might use the serial interface (UART), JTAG (if available), or other debugging interfaces. The core vulnerability here is the lack of secure boot in the firmware/hardware.
  • Impact: Complete device compromise, intellectual property theft, potential for reverse engineering and discovery of vulnerabilities.
  • Affected Component: Entire firmware, flash memory, UART/JTAG interfaces, bootloader (or lack thereof).
  • Risk Severity: High (if physical access is likely)
  • Mitigation Strategies:
    • Secure Boot (Firmware/Hardware): This is the primary mitigation. Enable secure boot to prevent unauthorized firmware modification. This requires both firmware and hardware support.
    • Flash Encryption (if supported by hardware and firmware): Encrypt the contents of the flash memory to protect the firmware from being read directly. This requires support from both the hardware and the firmware.
    • Physical Security: Enclose the device in a tamper-resistant enclosure (this is a physical mitigation, but important).
    • Disable Debug Interfaces: Physically disable or disconnect the UART and JTAG interfaces after development (this is a physical mitigation, but important).