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Ngrok API Key

An Ngrok API Key is a credential used to authenticate and authorize access to Ngrok's tunneling services. Ngrok provides secure tunnels to localhost, enabling developers to expose local servers to the internet for testing and development purposes. The exposure of an Ngrok API Key is a significant security concern because it can allow unauthorized users to create tunnels, potentially leading to unauthorized access to internal applications and services.

How Does It Look​

Ngrok API Keys can appear in various contexts, such as:

  • Environment variables:

    export NGROK_API_KEY="12345abcde"

  • Configuration files (JSON, YAML, .env):

    {
      "ngrok": {
        "api_key": "12345abcde"
      }
    }

  • Code snippets:

    ngrok.set_auth_token("12345abcde")

  • Connection strings:

    ngrok://12345abcde@ngrok.io

Severity​

  • 🟠 High

The Ngrok API Key provides access to create and manage tunnels, which can expose internal services to the internet. The blast radius includes potential unauthorized access to sensitive applications and data, depending on what is exposed through the tunnels.

What Can an Attacker Do?​

With immediate access to an Ngrok API Key, an attacker can create tunnels to expose internal services, potentially leading to unauthorized access.

Key actions an attacker can perform:

  • Create unauthorized tunnels: Expose internal applications to the internet (if the attacker knows the internal service endpoints).
  • Modify tunnel configurations: Change settings to redirect traffic or alter access controls (if the API Key has configuration permissions).
  • Access sensitive data: Intercept data transmitted through the tunnels (if the tunnels are not encrypted).
  • Monitor traffic: Capture and analyze traffic for further exploitation (if the attacker has access to the tunnel endpoints).

An attacker could escalate their access by using the tunnels to exploit vulnerabilities in exposed services, potentially leading to lateral movement within the network.

Real-World Impact​

The exposure of an Ngrok API Key poses significant business risks, including unauthorized access and data breaches.

Potential consequences include:

  • Data Exposure: Sensitive internal data could be accessed (if the tunnels expose databases or internal APIs).
  • Financial Loss: Costs associated with data breaches and incident response (if sensitive data is compromised).
  • Operational Disruption: Downtime or service interruptions (if critical services are exposed and attacked).
  • Reputational Damage: Loss of customer trust and brand reputation.

In a worst-case scenario, an attacker could use the tunnels to gain a foothold in the network, leading to widespread compromise and data exfiltration.

Prerequisites for Exploitation​

  • Network access requirements: Ability to connect to the internet to utilize Ngrok services.
  • Additional context needed: Knowledge of internal service endpoints to create effective tunnels.
  • Any rate limits or restrictions they'd face: Ngrok may impose rate limits on tunnel creation and usage.

How to Verify If It's Active​

To verify if an Ngrok API Key is active, use the following command:

ngrok authtoken [API_KEY]

Valid credential response: The command succeeds, and Ngrok confirms the API Key is set.

Invalid/expired credential response: The command fails with an error message indicating an invalid or expired API Key.

Detection Patterns​

Common Variable Names:

  • NGROK_API_KEY
  • NGROK_TOKEN
  • NGROK_AUTH_TOKEN
  • NGROK_KEY
  • NGROK_SECRET
  • NGROK_ACCESS_KEY

File Locations:

  • .env
  • config.json
  • settings.yaml
  • ngrok-config.yml
  • credentials.txt

Regex Pattern:

ngrok[a-zA-Z0-9]{20,40}

Remediation Steps​

  1. Revoke immediately - Go to Ngrok Dashboard > API Keys and delete the compromised key.
  2. Audit access logs - Review Ngrok logs for unauthorized tunnel creations or modifications during the exposure window.
  3. Assess blast radius - Identify all systems, applications, and environments that used the exposed API Key.
  4. Rotate credential - Generate a new API Key in the Ngrok Dashboard with least-privilege permissions.
  5. Update dependent systems - Deploy the new API Key to all applications and update CI/CD pipelines securely.
  6. Harden access controls - Enable IP restrictions and require authentication for tunnels in Ngrok settings.
  7. Implement secrets management - Migrate API Keys to a secrets manager (HashiCorp Vault, AWS Secrets Manager) to prevent hardcoding.
  8. Add detection controls - Set up pre-commit hooks and repository scanning to catch credential leaks before they reach production.

Credential exposures often go undetected for extended periods, increasing the window for exploitation. As a long-term strategy, plan to establish an internal process or engage an external vendor for continuous external exposure monitoring. This helps identify leaked secrets across public repositories, paste sites, dark web forums, and other external sources before attackers can leverage them. Proactive detection and rapid response are essential to minimizing the impact of credential leaks.

References​