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attack-surface.md

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Attack Surface Analysis for inconshreveable/ngrok

Attack Surface: 1. Unintentional Service Exposure

  • Description: Exposing services that were never intended for public access.
  • How ngrok Contributes: ngrok bypasses network firewalls and NAT, making any listening port on the local machine potentially accessible from the internet. This is ngrok's core function, and thus directly contributes.
  • Example: A developer accidentally starts ngrok pointing to a local database server (e.g., port 3306 for MySQL) that contains sensitive customer data, without any authentication.
  • Impact: Unauthorized access to sensitive data, potential data breaches, complete system compromise.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Strict Port Control: Explicitly specify the exact port and local address (e.g., 127.0.0.1:8080) to be exposed via ngrok's configuration. Avoid exposing entire ranges or default ports.
    • Service Hardening: Ensure all services running on the machine, even those not intended for public access, are configured securely with strong authentication and authorization. This is a general best practice, but ngrok's exposure makes it critical.
    • Firewall Rules: Configure local firewall rules (even with ngrok in use) to restrict access to sensitive ports from all sources except localhost. This provides a layer of defense even if ngrok is misconfigured.
    • Principle of Least Privilege: Run ngrok and the target application with the minimum necessary privileges.

Attack Surface: 2. Vulnerable Service Exposure

  • Description: Exposing a service that has known or unknown vulnerabilities.
  • How ngrok Contributes: Provides a direct, publicly accessible route to the vulnerable service, bypassing network-level protections that might otherwise mitigate the risk. ngrok makes the vulnerability reachable.
  • Example: Exposing an outdated version of a web application with a known remote code execution (RCE) vulnerability via ngrok.
  • Impact: Remote code execution, data breaches, denial of service, complete system compromise.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Regular Patching: Keep the exposed service and all its dependencies up-to-date with the latest security patches. This is always important, but ngrok's exposure makes it critical.
    • Vulnerability Scanning: Regularly scan the exposed service for known vulnerabilities.
    • Secure Configuration: Follow security best practices for configuring the exposed service (e.g., disabling unnecessary features, using strong passwords).
    • Web Application Firewall (WAF): Consider using a WAF to filter malicious traffic and protect against common web application attacks. While the WAF isn't directly related to ngrok, it's a crucial mitigation because ngrok exposes the service.

Attack Surface: 3. Compromised ngrok Client/Authtoken

  • Description: An attacker gains control of the ngrok client or the authtoken.
  • How ngrok Contributes: The ngrok client and authtoken are the direct control mechanisms for the tunnel. Compromise of these is a compromise of ngrok itself.
  • Example: An attacker steals the ngrok authtoken from a developer's .bash_history file or a compromised CI/CD pipeline.
  • Impact: The attacker can create new tunnels, redirect traffic, expose additional services, and potentially access other resources on the local network through the compromised ngrok instance.
  • Risk Severity: High
  • Mitigation Strategies:
    • Secure Authtoken Storage: Store the authtoken securely using environment variables or a dedicated secrets management solution. Never commit it to version control. This directly protects the ngrok credential.
    • Regular Authtoken Rotation: Periodically rotate the ngrok authtoken. This limits the window of opportunity for an attacker using a stolen token.
    • Endpoint Protection: Protect the machine running the ngrok client with strong endpoint security measures (antivirus, EDR). This reduces the risk of the client itself being compromised.
    • Multi-Factor Authentication (MFA): If possible, enable MFA for the ngrok account. This adds an extra layer of protection against unauthorized access to the ngrok account.
    • Least Privilege: Run the ngrok client with a dedicated, non-privileged user account.

Attack Surface: 4. Man-in-the-Middle (MitM) Attacks (without HTTPS)

  • Description: An attacker intercepts and potentially modifies traffic between the client and the exposed service.
  • How ngrok Contributes: If ngrok is used to expose an HTTP service (without TLS), the traffic is unencrypted through the ngrok tunnel. ngrok is the conduit for the vulnerable traffic.
  • Example: An attacker on a public Wi-Fi network intercepts the unencrypted HTTP traffic between a user and an ngrok tunnel, stealing login credentials.
  • Impact: Data interception, credential theft, session hijacking, injection of malicious content.
  • Risk Severity: High
  • Mitigation Strategies:
    • Always Use HTTPS: Never expose services over plain HTTP via ngrok. Ensure the exposed service is configured to use HTTPS with a valid TLS certificate. This encrypts the traffic through the ngrok tunnel.
    • End-to-End Encryption: Terminate TLS on your server, not at the ngrok edge, to ensure that ngrok only sees encrypted traffic. This provides the strongest protection.