Skip to main content

Mandrill API Key

Mandrill is a transactional email API for Mailchimp users, allowing businesses to send personalized, one-to-one e-commerce emails and automated transactional emails. An API key for Mandrill is a credential that grants access to the Mandrill API, enabling the sending of emails, managing templates, and accessing account data. Exposure of this key is a significant security concern as it can lead to unauthorized access to email sending capabilities, potentially resulting in spam, phishing attacks, or unauthorized data access.

How Does It Look​

Mandrill API keys can appear in various contexts, such as:

  • Environment variables:

    export MANDRILL_API_KEY="mandrill-1234567890abcdef"

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

    {
      "mandrill": {
        "apiKey": "mandrill-1234567890abcdef"
      }
    }
    mandrill:
      apiKey: mandrill-1234567890abcdef
    MANDRILL_API_KEY=mandrill-1234567890abcdef

  • Code snippets:

    mandrill_client = MandrillClient(api_key="mandrill-1234567890abcdef")

Severity​

  • 🟠 High

The severity of a Mandrill API key exposure is high because it allows unauthorized users to send emails on behalf of the account, potentially leading to spam or phishing attacks. The blast radius includes the potential for reputational damage and blacklisting of email domains, affecting email deliverability.

What Can an Attacker Do?​

With immediate access to a Mandrill API key, an attacker can:

  • Send unauthorized emails: Send spam or phishing emails (if the key has email sending permissions).
  • Access account data: Retrieve email templates and logs (if the key has read permissions).
  • Modify email templates: Alter existing templates to include malicious content (if the key has write permissions).
  • Monitor email activity: Track email statistics and recipient interactions (if the key has analytics access).

An attacker could escalate their access by using the compromised key to gather information about the account's email practices, potentially leading to further exploitation or lateral movement within the organization's email infrastructure.

Real-World Impact​

Exposure of a Mandrill API key poses significant business risks:

The primary impact includes unauthorized email sending, which can lead to:

  • Data Exposure: Email content and recipient information (if the key has access to email logs).
  • Financial Loss: Costs associated with increased email sending or account suspension (if billing is affected by unauthorized usage).
  • Operational Disruption: Email deliverability issues due to domain blacklisting (if spam is sent using the key).
  • Reputational Damage: Loss of trust from customers and partners due to spam or phishing emails.

In worst-case scenarios, the exposure could lead to cascading effects, such as compromised customer accounts or further breaches if phishing emails are successful.

Prerequisites for Exploitation​

To exploit a Mandrill API key, an attacker needs:

  • Network access: Ability to make API requests to Mandrill's servers.
  • Additional context: Knowledge of the account's email practices or templates to craft convincing emails.
  • Rate limits: Awareness of any rate limits that might restrict the volume of emails sent.

How to Verify If It's Active​

To verify if a Mandrill API key is active, use the following command:

curl -X GET "https://mandrillapp.com/api/1.0/users/ping.json" -d '{"key":"[API_KEY]"}'

Valid credential response: A successful response will return a status message indicating the key is active.

Invalid/expired credential response: An error message indicating authentication failure or invalid API key.

Detection Patterns​

Common Variable Names:

  • MANDRILL_API_KEY
  • MANDRILL_KEY
  • API_KEY
  • MANDRILL_SECRET
  • MANDRILL_TOKEN
  • MANDRILL_API_TOKEN

File Locations:

  • .env
  • config.json
  • settings.yaml
  • appsettings.json
  • credentials.txt

Regex Pattern:

mandrill-[a-f0-9]{16}

Remediation Steps​

  1. Revoke immediately - Go to Mandrill's API settings and delete the compromised API key.
  2. Audit access logs - Review Mandrill's activity logs for unauthorized email sending or template 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 Mandrill and ensure it has 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 allowlisting in Mandrill and require API key usage only from trusted networks.
  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​