# Credential Exfiltration via User-Controlled Endpoint

- ID: python-webhook-credential-exfiltration
- Severity: CRITICAL
- CWE: CWE-201 (CWE-201)
- Languages: Python
- Frameworks: flask, django, fastapi

## Description

Detects when internal credentials (API keys, secrets, tokens) are sent in HTTP requests
to user-controlled endpoints. This allows attackers to exfiltrate server credentials
by providing a malicious webhook URL that captures the sensitive headers or body data.

Example vulnerable pattern:
```python
# User controls 'endpoint' from request
endpoint = request.form.get('webhook_url')

# Server sends its internal API key to attacker-controlled URL
requests.post(endpoint, headers={'X-API-Key': os.environ['INTERNAL_API_KEY']})
```

This is different from standard SSRF (which accesses internal resources) - here the attacker
exfiltrates server credentials to their own controlled endpoint.

## Detection Message

User input from {source} controls the destination of an HTTP request at {sink}.
If credentials are included in the request headers or body, attackers can exfiltrate
them by providing a malicious endpoint URL.

## Remediation

1. Never send internal credentials to user-controlled endpoints
2. Validate webhook URLs against a strict allowlist of trusted domains
3. Use webhook secrets for authentication instead of sending API keys

```python
from urllib.parse import urlparse

ALLOWED_WEBHOOK_DOMAINS = {'api.slack.com', 'hooks.stripe.com'}

def send_webhook(webhook_url, data):
    parsed = urlparse(webhook_url)
    if parsed.hostname not in ALLOWED_WEBHOOK_DOMAINS:
        raise ValueError('Untrusted webhook domain')

    # Use webhook-specific secret, not internal API key
    requests.post(webhook_url, json=data,
                  headers={'X-Webhook-Secret': user_webhook_secret})
```

Learn more: https://shoulder.dev/learn/python/cwe-201/credential-exfiltration

## Documentation

[object Object]

## Related Rules

- **Credential Exfiltration via User-Controlled Endpoint** [CRITICAL]: 
- **Credential Exfiltration via User-Controlled Endpoint** [CRITICAL]: