# Credential Exfiltration via User-Controlled Endpoint

- ID: javascript-webhook-credential-exfiltration
- Severity: CRITICAL
- CWE: CWE-201 (CWE-201)
- Languages: JavaScript, TypeScript
- Frameworks: express, fastify, nodejs, nextjs, nestjs, koa, hapi

## 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:
```javascript
// User controls 'endpoint' from request
const endpoint = req.body.webhookUrl;

// Server sends its internal API key to attacker-controlled URL
await fetch(endpoint, {
  headers: { 'X-API-Key': process.env.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

```javascript
// SAFE: Validate webhook URL against allowlist
const ALLOWED_WEBHOOK_DOMAINS = ['api.slack.com', 'hooks.stripe.com'];

const webhookUrl = new URL(req.body.webhookUrl);
if (!ALLOWED_WEBHOOK_DOMAINS.includes(webhookUrl.hostname)) {
  return res.status(400).json({ error: 'Untrusted webhook domain' });
}

// SAFE: Use webhook-specific secret, not internal API key
await fetch(webhookUrl, {
  headers: { 'X-Webhook-Secret': req.body.webhookSecret }
});
```

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

## Documentation

[object Object]

## Related Rules

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