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Mitigation Strategies Analysis for stripe/stripe-python

Mitigation Strategy: Secure Secret Key Management (via stripe-python)

  • Description:

    1. Never Hardcode: Ensure the Stripe secret key is never present in your source code.
    2. Environment Variable Loading: Use os.environ.get("STRIPE_SECRET_KEY") to load the key from an environment variable within your Python code, immediately before initializing the stripe library: 
      import os
import stripe

stripe.api_key = os.environ.get("STRIPE_SECRET_KEY")
if stripe.api_key is None:
    raise Exception("Stripe secret key not found!")
    3. Secrets Management (Advanced): For production, integrate with a secrets manager (AWS Secrets Manager, etc.) and retrieve the key programmatically, then set stripe.api_key.
    4. No .env in Production: If using .env for local development, ensure it's never committed (use .gitignore).
    5. Key Rotation: Rotate keys via the Stripe Dashboard and update the environment variable/secrets manager.

  • Threats Mitigated:

    • Secret Key Exposure (Severity: Critical): Direct access to your Stripe account.
    • Accidental Commits (Severity: High): Public exposure of the key.
    • Unauthorized Access (Severity: High): Compromise of your server/environment.

  • Impact:

    • Secret Key Exposure: Risk reduced from Critical to Low.
    • Accidental Commits: Risk eliminated (with proper .gitignore).
    • Unauthorized Access: Risk significantly reduced.

  • Currently Implemented:

    • Environment variables used in payments_service/config.py.
    • .env file used locally, included in .gitignore.

  • Missing Implementation:

    • Key rotation not implemented.
    • reporting_service hardcodes the key (in reporting_service/stripe_client.py - CRITICAL).
    • No secrets management service; environment variables used in production.

Mitigation Strategy: Pin and Update API Version (using stripe.api_version)

  • Description:

    1. Explicit Versioning: Always set stripe.api_version explicitly in your Python code: 
      import stripe
stripe.api_version = "2023-10-16"  # Use a specific, stable version
    2. Don't Rely on Defaults: Never rely on the stripe-python library's default API version.
    3. Regular Review: Periodically check Stripe's API changelog.
    4. Update and Test: When updating, change stripe.api_version and thoroughly test.

  • Threats Mitigated:

    • Breaking Changes (Severity: Medium): API updates breaking your integration.
    • Deprecated Feature Exploits (Severity: Medium to High): Using vulnerable, deprecated features.
    • Unexpected Behavior (Severity: Low to Medium): Inconsistent behavior due to default version changes.

  • Impact:

    • Breaking Changes: Risk significantly reduced.
    • Deprecated Feature Exploits: Risk reduced.
    • Unexpected Behavior: Risk minimized.

  • Currently Implemented:

    • stripe.api_version set in payments_service/config.py.

  • Missing Implementation:

    • No regular API review process.
    • subscriptions_service uses the library default.

Mitigation Strategy: Verify Webhook Signatures (with stripe.Webhook.construct_event())

  • Description:

    1. Webhook Secret: Get your endpoint secret from the Stripe Dashboard.
    2. Signature Verification: Always use stripe.Webhook.construct_event() to verify signatures in your webhook handler: 
      from flask import request, jsonify
import stripe
import os

stripe.api_key = os.environ.get("STRIPE_SECRET_KEY")
endpoint_secret = os.environ.get("STRIPE_WEBHOOK_SECRET")

@app.route('/webhook', methods=['POST'])
def webhook():
    payload = request.data
    sig_header = request.headers['STRIPE_SIGNATURE']

    try:
        event = stripe.Webhook.construct_event(
            payload, sig_header, endpoint_secret
        )
    except ValueError as e:
        return jsonify({'error': str(e)}), 400  # Invalid payload
    except stripe.error.SignatureVerificationError as e:
        return jsonify({'error': str(e)}), 400  # Invalid signature

    # ... process the event (ONLY if verification succeeds) ...
    return jsonify({'success': True})
    3. Exception Handling: Handle ValueError and stripe.error.SignatureVerificationError correctly. Do not process the event if verification fails.
    4. HTTPS: Use HTTPS for your webhook endpoint.
    5. Idempotency: Implement idempotency handling.

  • Threats Mitigated:

    • Webhook Spoofing (Severity: High): Fake requests triggering actions.
    • Data Tampering (Severity: High): Modification of webhook data.

  • Impact:

    • Webhook Spoofing: Risk eliminated (with correct verification).
    • Data Tampering: Risk eliminated (with correct verification).

  • Currently Implemented:

    • Verification in webhook_handler/handler.py.
    • HTTPS used.

  • Missing Implementation:

    • Idempotency handling is missing.

Mitigation Strategy: Handle Stripe API Errors (using stripe.error.* exceptions)

  • Description:

    1. try...except Blocks: Wrap all stripe-python API calls in try...except blocks.
    2. Specific Exceptions: Catch specific stripe.error.* exceptions: 
      import stripe

try:
    # Stripe API call (e.g., stripe.Charge.create(...))
    pass
except stripe.error.CardError as e:
    # Handle card errors (user-friendly message)
    print(f"Card Error: {e}")
except stripe.error.RateLimitError as e:
    # Handle rate limits (retry with backoff)
    print(f"Rate Limit Error: {e}")
except stripe.error.APIConnectionError as e:
    # Handle connection issues (retry, inform user)
    print(f"API Connection Error: {e}")
except stripe.error.AuthenticationError as e:
    # Handle authentication errors (check API key)
    print(f"Authentication Error: {e}")
except stripe.error.InvalidRequestError as e:
    # Handle invalid requests (log for debugging)
    print(f"Invalid Request Error: {e}")
except stripe.error.StripeError as e:
    # Handle other Stripe errors
    print(f"Stripe Error: {e}")
except Exception as e:
    # Catch any other unexpected errors
    print(f"Unexpected Error: {e}")
    3. Appropriate Handling: Implement logic for each exception type (user messages, retries, logging).
    4. Sanitized Logging: Log errors, but never log sensitive data.
    5. Generic Exception: Catch Exception for unexpected errors.

  • Threats Mitigated:

    • Application Crashes (Severity: Medium): Unhandled exceptions.
    • Information Disclosure (Severity: Medium to High): Exposing sensitive error details.
    • Unexpected Behavior (Severity: Low to Medium): Incorrect error handling.

  • Impact:

    • Application Crashes: Risk significantly reduced.
    • Information Disclosure: Risk significantly reduced (with sanitization).
    • Unexpected Behavior: Risk reduced.

  • Currently Implemented:

    • Basic try...except in payments_service/processor.py.

  • Missing Implementation:

    • Specific stripe.error.* exceptions not consistently handled.
    • Inconsistent and potentially insecure error logging.
    • No retry logic.
    • Limited error handling in subscriptions_service.

Mitigation Strategy: Keep stripe-python Updated

  • Description:

    1. Dependency Management: Use pip, poetry, or pipenv.
    2. Regular Updates: Update stripe-python regularly:
      • pip: pip install --upgrade stripe
      • poetry: poetry update stripe
      • pipenv: pipenv update stripe
    3. Vulnerability Scanning: Use pip-audit, Snyk, or Dependabot.
    4. Test After Updates: Thoroughly test after any update.

  • Threats Mitigated:

    • Known Vulnerabilities (Severity: Varies, potentially Critical): Exploits in older library versions.

  • Impact:

    • Known Vulnerabilities: Risk significantly reduced.

  • Currently Implemented:

    • requirements.txt used.
    • Manual updates, but not regular.

  • Missing Implementation:

    • No automated vulnerability scanning.
    • No regular update schedule.