• CWE-1277: Firmware Not Updateable

Das Produkt bietet seinen Nutzern keine Möglichkeit, seine Firmware zu aktualisieren oder zu patchen, um eventuelle Schwachstellen oder Sicherheitslücken zu beheben.

CWE-1277: Firmware Not Updateable

CWE ID: 1277
Name: Firmware Not Updateable

Beschreibung

Das Produkt bietet seinen Nutzern keine Möglichkeit, seine Firmware zu aktualisieren oder zu patchen, um eventuelle Schwachstellen oder Sicherheitslücken zu beheben.

Erweiterte Beschreibung

Ohne die Möglichkeit, Firmware zu patchen oder zu aktualisieren, bleiben Nutzer anfällig für die Ausnutzung bekannter Schwachstellen oder solcher, die in der Zukunft entdeckt werden. Dies kann sie während der gesamten Lebensdauer des Geräts, die Jahre oder Jahrzehnte betragen kann, einem permanenten Risiko aussetzen. Es können externe Schutzmaßnahmen und mitigations eingesetzt werden, um das Risiko eines bösartigen Angriffs zu verhindern oder zu reduzieren, jedoch kann die grundlegende Schwäche nicht behoben werden.

Risikominderungsmaßnahmen

Maßnahme (Requirements)

Effektivität: Unknown
Beschreibung: Um die Möglichkeit zur Firmware-Aktualisierung zu gewährleisten, sind folgende Anforderungen zu berücksichtigen:

  1. Firmware-Update-Mechanismus: Es muss ein sicherer Mechanismus für die Übertragung und Installation von Firmware-Updates implementiert werden. Dieser Mechanismus sollte über eine definierte Schnittstelle zugänglich sein und die Möglichkeit bieten, Updates sowohl über das Internet (z.B. via OTA - Over-the-Air) als auch über lokale Medien (z.B. USB) zu installieren.

  2. Integritätsprüfung: Vor der Installation muss eine Integritätsprüfung der Firmware durchgeführt werden, um sicherzustellen, dass die Firmware nicht manipuliert wurde. Dies kann durch die Verwendung von kryptografischen Hash-Funktionen (z.B. SHA-256) und die Verifizierung gegen einen bekannten, vertrauenswürdigen Hash-Wert erfolgen.

  3. Authentifizierung: Die Firmware-Updates müssen authentifiziert werden, um sicherzustellen, dass sie von einer vertrauenswürdigen Quelle stammen. Dies kann durch die Verwendung digitaler Signaturen erfolgen, wobei der öffentliche Schlüssel des Herausgebers der Firmware-Updates in das Gerät integriert wird. Die Installation sollte nur dann erfolgen, wenn die Signatur verifiziert werden kann.

  4. Rollback-Schutz: Es sollte ein Mechanismus implementiert werden, der das Zurücksetzen auf ältere Firmware-Versionen (Rollback) verhindert, um zu verhindern, dass Angreifer eine anfällige Version wiederherstellen können.

  5. Sichere Speicherung von Schlüsseln: Die für die Authentifizierung und Integritätsprüfung verwendeten privaten Schlüssel müssen sicher gespeichert und vor unbefugtem Zugriff geschützt werden. Hardware Security Modules (HSMs) oder Secure Elements (SEs) können hierfür in Betracht gezogen werden.

  6. Versionsmanagement: Ein robustes Versionsmanagement-System ist erforderlich, um Firmware-Versionen zu verfolgen, zu verwalten und zu verteilen.

  7. Audit-Protokollierung: Die Installation von Firmware-Updates sollte protokolliert werden, um eine Nachverfolgung und Analyse im Falle von Sicherheitsvorfällen zu ermöglichen.

Maßnahme (Architecture and Design)

Effektivität: Unknown
Beschreibung: ## Device Firmware Update Design Specification

This document outlines the design for enabling firmware updates on the device, focusing on secure distribution, integrity verification, and authentication.

1. Firmware Update Architecture:

  • Dual-Bank Flash Memory: The device will utilize a dual-bank flash memory architecture. One bank (Bank A) will run the current firmware, while the other (Bank B) will receive the new firmware during the update process. This allows for a fail-safe mechanism – if the new firmware fails to boot, the device can revert to the previous, known-good version.
  • Bootloader: A dedicated, secure bootloader will reside in ROM and be responsible for initiating and managing the firmware update process. This bootloader will be immutable and designed for minimal functionality, solely focused on update management.
  • Update Server: A designated, secure Update Server will host the firmware updates. This server will be hardened and protected against unauthorized access.

2. Firmware Distribution:

  • OTA (Over-the-Air) Updates: The primary distribution method will be OTA updates via a secure HTTPS connection. The device will periodically check for updates from the Update Server.
  • Local Media Updates (Optional): Support for firmware updates via USB or SD card will be provided as an optional feature, primarily for scenarios with limited network connectivity. This method will require manual initiation and will be subject to the same integrity and authentication checks as OTA updates.
  • Signed Firmware Packages: Firmware updates will be distributed as signed packages containing the firmware image and a digital signature.

3. Integrity Verification:

  • Hashing: Before transferring the firmware image to Bank B, the device will calculate a cryptographic hash (SHA-256) of the received firmware package.
  • Hash Comparison: The device will compare the calculated hash with a pre-calculated hash value provided by the Update Server. The update process will only proceed if the hashes match.
  • Secure Hash Storage: The pre-calculated hash value will be stored securely within the device, ideally within a Hardware Security Module (HSM) or Secure Element (SE) to prevent tampering.

4. Authentication:

  • Digital Signatures: Firmware packages will be digitally signed by the manufacturer using a private key.
  • Public Key Embedded: The device will have the manufacturer’s public key embedded during manufacturing. This public key will be used to verify the digital signature on the firmware package.
  • Signature Verification: The bootloader will verify the digital signature before proceeding with the update. The update process will be aborted if the signature verification fails.
  • Certificate Revocation List (CRL): A CRL mechanism will be implemented to allow for the revocation of compromised signing keys. The device will periodically check the CRL to ensure that the signing key used to sign the firmware package is still valid.

5. Update Process Flow:

  1. Check for Updates: The device periodically checks the Update Server for new firmware versions.
  2. Download Firmware Package: If a new version is available, the device downloads the firmware package.
  3. Integrity Verification: The device calculates the hash of the downloaded package and compares it with the expected hash.
  4. Authentication: The device verifies the digital signature using the embedded public key.
  5. Firmware Transfer: If both integrity and authentication checks pass, the firmware image is transferred to Bank B.
  6. Switch Banks: After successful transfer, the device switches to Bank B for the next boot cycle.
  7. Boot and Validation: During the next boot, the device validates the new firmware. If validation fails, the device reverts to Bank A.

6. Security Considerations:

  • Secure Communication: All communication with the Update Server must be encrypted using TLS/SSL.
  • Code Signing: All code involved in the update process must be digitally signed to prevent unauthorized modifications.
  • Tamper Detection: Implement tamper detection mechanisms to detect physical tampering with the device.
  • Regular Security Audits: Conduct regular security audits of the firmware update process to identify and address potential vulnerabilities.

This design aims to provide a robust and secure mechanism for updating the device firmware, minimizing the risk of unauthorized modifications and ensuring the integrity and authenticity of the updates.

Maßnahme (Implementation)

Effektivität: Unknown
Beschreibung: Okay, let’s outline the implementation steps for the firmware update functionality, building upon the design specification. This will be a high-level guide, as the specifics will depend heavily on the microcontroller/processor architecture, flash memory type, and development environment. I’ll break it down into hardware, bootloader, firmware, and testing aspects. I’ll also include pseudo-code snippets where appropriate.

1. Hardware Considerations:

  • Dual-Bank Flash: Ensure the hardware supports dual-bank flash memory and the ability to switch between them. This often involves specific memory controller configuration.
  • Communication Interface: Implement the necessary communication interface (e.g., UART, Ethernet, Wi-Fi) for connecting to the Update Server.
  • Secure Storage: A Hardware Security Module (HSM) or Secure Element (SE) is highly recommended for storing the public key and other sensitive data. If not available, a secure region within the flash memory can be used, but with reduced security.
  • Debug/Recovery Interface: A JTAG or similar debug interface is crucial for recovery in case of a failed firmware update.

2. Bootloader Implementation:

The bootloader is the most critical component. It needs to be small, reliable, and secure.

  • Initialization:
    • Initialize the communication interface (UART, Ethernet, Wi-Fi).
    • Initialize the flash memory controller.
    • Check for a valid firmware update in Bank B.
  • Update Check:
    • Periodically check the Update Server for new firmware versions.
    • Download the firmware package.
  • Integrity Verification: 
    received_hash = calculate_hash(received_firmware_package)
if received_hash != expected_hash:
    print("Integrity check failed!")
    halt_system()
  • Authentication: 
    signature = extract_signature(received_firmware_package)
if verify_signature(signature, received_firmware_package, public_key):
    print("Authentication successful!")
else:
    print("Authentication failed!")
    halt_system()
  • Firmware Transfer:
    • Erase Bank B.
    • Write the received firmware package to Bank B.
  • Bank Switching:
    • Switch the boot bank to Bank B.
  • Error Handling:
    • Implement robust error handling for communication errors, memory write failures, and authentication failures.
    • Provide a mechanism for reverting to the previous firmware version in case of a failed update.

3. Firmware Implementation (Main Application):

  • Update Status Reporting: Provide a mechanism for the main application to query the bootloader for the update status.
  • Rollback Mechanism (Optional): If the main application detects a problem with the new firmware, it can trigger a rollback to the previous version. This requires a mechanism for the main application to communicate with the bootloader.

4. Key Functions & Pseudo-Code Examples (Illustrative):

  • check_for_updates():

    response = send_request_to_update_server("GET /api/firmware/latest")
if response.status_code == 200:
    latest_version = response.data.version
    if latest_version > current_version:
        return latest_version
    else:
        return null
    else:
        return null
else:
    return null

  • download_firmware(version):

    url = "https://updateserver.com/firmware/version_" + version + ".bin"
response = send_request_to_url(url)
if response.status_code == 200:
    return response.data
else:
    return null

  • verify_signature(signature, data, public_key): (Uses cryptographic library)

    return crypto_library.verify(signature, data, public_key)

5. Testing & Validation:

  • Unit Tests: Test individual functions within the bootloader and firmware.
  • Integration Tests: Test the interaction between the bootloader and firmware.
  • System Tests: Test the entire firmware update process from start to finish.
  • Failover Testing: Simulate update failures (e.g., corrupted data, authentication failures) to ensure the system can recover gracefully.
  • Security Testing: Attempt to bypass the authentication and integrity checks to identify vulnerabilities.
  • Regression Testing: After any changes, re-run all tests to ensure no existing functionality has been broken.

Important Considerations:

  • Security: Protect the public key and other sensitive data. Use secure communication protocols (e.g., HTTPS).
  • Atomicity: Ensure that the firmware update process is atomic. If an error occurs during the update, the system should revert to a known good state.
  • Power Loss Protection: Implement mechanisms to protect against power loss during the update process. This might involve using a battery-backed RAM or a flash memory controller with power-loss protection.
  • Code Size: The bootloader must be small enough to fit in a limited amount of memory.
  • Real-Time Constraints: The bootloader must be able to complete the update process within a reasonable amount of time.

To provide more specific guidance, I need to know:

  • Microcontroller/Processor: (e.g., ARM Cortex-M4, ESP32, AVR)
  • Flash Memory Type: (e.g., NOR flash, NAND flash, SPI flash)
  • Development Environment: (e.g., Arduino IDE, Keil, IAR)
  • Communication Interface: (e.g., UART, Ethernet, Wi-Fi)
  • Security Requirements: (e.g., level of authentication, encryption)