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attack-surface.md

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Attack Surface Analysis for stjohnjohnson/smartthings-mqtt-bridge

Attack Surface: 1. MQTT Connection Interception (TLS/SSL Configuration within the Bridge)

Description: Attackers intercept the communication between the bridge and the MQTT broker due to misconfiguration within the bridge itself.

  • Contribution: The bridge is directly responsible for establishing a secure (or insecure) connection based on its configuration.
  • Example: The mqtt_port is set to 1883 (non-TLS) and TLS-related settings (mqtt_tls_ca_certs, etc.) are left blank in the bridge's config.yml.
  • Impact:
    • Eavesdropping on all SmartThings events and commands.
    • Ability to inject malicious commands by modifying intercepted traffic.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • (Developer/User): Always use TLS/SSL. Configure mqtt_port to a TLS-enabled port (e.g., 8883) in the bridge's configuration.
    • (Developer/User): Properly configure mqtt_tls_ca_certs, mqtt_tls_certfile, and mqtt_tls_keyfile in the bridge's configuration.
    • (Developer): Make TLS/SSL the default configuration and provide clear, prominent instructions. Issue a warning if the bridge starts up with an insecure configuration.

Attack Surface: 2. SmartThings API Token Leakage (Bridge Configuration/Storage)

Description: The smartthings_token used by the bridge is compromised due to insecure handling by the bridge or its configuration.

  • Contribution: The bridge stores and uses this token; its security is the bridge's responsibility.
  • Example: The config.yml file containing the token has overly permissive file permissions, allowing other users on the system to read it.
  • Impact:
    • An attacker can directly interact with the SmartThings API, bypassing the bridge.
    • Full control over SmartThings devices.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • (Developer/User): Store the smartthings_token securely in the configuration file. Ensure the file has restricted permissions (e.g., chmod 600 config.yml).
    • (Developer): Consider using environment variables instead of a configuration file for the token.
    • (Developer): Explore more robust secret management solutions for production deployments.

Attack Surface: 3. MQTT Message Injection (Lack of Validation within the Bridge)

Description: Attackers inject malicious MQTT messages that are not properly validated by the bridge's code.

  • Contribution: The bridge is directly responsible for parsing and validating all incoming MQTT messages before acting on them.
  • Example: An attacker sends a crafted MQTT message with a command payload designed to trigger a buffer overflow in the bridge's message handling code.
  • Impact:
    • Potential for remote code execution on the system running the bridge.
    • Denial-of-service.
    • Manipulation of SmartThings devices through crafted commands.
  • Risk Severity: High
  • Mitigation Strategies:
    • (Developer): Implement strict input validation for all incoming MQTT messages. Sanitize and validate data before passing it to SmartThings or acting upon it.
    • (Developer): Define a clear schema for expected MQTT message formats and reject any messages that do not conform.
    • (Developer): Implement rate limiting on incoming messages to mitigate flooding attacks.

Attack Surface: 4. Overly Permissive SmartApp Capabilities (Defined by the Bridge's SmartApp)

Description: The SmartApp associated with the bridge requests more permissions than it needs, increasing the impact of a bridge compromise.

  • Contribution: The bridge's functionality and potential attack surface are directly defined by the capabilities requested by its associated SmartApp.
  • Example: The SmartApp requests capability.switchLevel.* (control of dimming) when it only needs capability.switch.* (on/off control).
  • Impact: If the bridge is compromised, the attacker gains access to all capabilities granted to the SmartApp, not just those strictly necessary.
  • Risk Severity: High
  • Mitigation Strategies:
    • (Developer): Strictly adhere to the principle of least privilege. The SmartApp should only request the absolute minimum capabilities required for the bridge to function.
    • (Developer): Clearly document the required capabilities and why they are needed.

Attack Surface: 5. Dependency Vulnerabilities (Directly Affecting the Bridge)

Description: The bridge uses external libraries that have known vulnerabilities.

  • Contribution: The bridge's code directly depends on these libraries; their vulnerabilities become the bridge's vulnerabilities.
  • Example: An outdated version of the Paho MQTT client library is used, which has a known remote code execution vulnerability.
  • Impact: Attackers can exploit vulnerabilities in the dependencies to compromise the bridge itself.
  • Risk Severity: High (severity depends on the specific vulnerability)
  • Mitigation Strategies:
    • (Developer): Regularly update all dependencies to their latest secure versions.
    • (Developer): Use a dependency management tool and integrate vulnerability scanning into the development process.