Zone Transfer in Express with Cockroachdb

A DNS zone transfer (AXFR) abuse scenario in an Express application using CockroachDB typically arises when the application exposes administrative or debugging endpoints that interact with DNS and database controls. While CockroachDB itself does not serve DNS, an Express service might use DNS queries—for example, to discover backend nodes or service discovery—and combine that with database operations in a way that allows an unauthenticated attacker to trigger unintended behavior or data exposure.

In this combination, a misconfigured Express route might accept a hostname parameter, perform a DNS lookup, and then use that result to build a CockroachDB query without proper validation. If the route also allows DNS query responses to be returned to the caller (e.g., for debugging), an attacker can request a zone transfer-style response or use the endpoint to probe internal hostnames. Because the scan includes checks for BOLA/IDOR and Unsafe Consumption, the scanner can detect whether an endpoint allows data leakage across tenants or exposes administrative functionality without authentication.

For example, an Express route that directly concatenates user input into a DNS lookup and then uses the result in a CockroachDB SQL string can lead to information exposure or indirect SSRF. The scanner’s checks for Input Validation, Property Authorization, and SSRF run in parallel and will flag unsafe dynamic construction of queries and uncontrolled external interactions. Even though CockroachDB does not initiate DNS transfers, the route’s behavior—accepting a hostname, resolving it, and using it in a database call—creates a chain that can expose sensitive data or enable unauthorized operations when combined with weak authorization and insufficient input validation.

Because middleBrick scans the unauthenticated attack surface and compares findings against frameworks like OWASP API Top 10 and PCI-DSS, it will highlight routes that allow data exposure via unsafe DNS and database interactions. The scanner’s LLM/AI Security checks further ensure that no endpoint unintentionally leaks system-level information that could aid an attacker in crafting further attacks against the CockroachDB-backed services.

To remediate zone transfer style issues in Express when interacting with CockroachDB, validate and sanitize all inputs, avoid dynamic query building, and enforce strict authorization. Use parameterized queries and ensure DNS interactions are limited to trusted, non-user-controlled sources.

Example: Safe endpoint with validation and parameterized queries

const express = require('express');
const { Pool } = require('pg');
const app = express();

// CockroachDB connection string from environment
const pool = new Pool({
  connectionString: process.env.DATABASE_URL,
});

// Whitelist of allowed services for lookup; avoid dynamic hostnames from users
const ALLOWED_SERVICE = new Set(['service-a.example.com', 'service-b.example.com']);

app.get('/api/tenant-config', async (req, res) => {
  const { serviceName, tenantId } = req.query;

  // Validate tenantId is a valid UUID (example pattern)
  if (!tenantId || !/^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i.test(tenantId)) {
    return res.status(400).json({ error: 'Invalid tenant ID' });
  }

  // Enforce whitelist for serviceName; do not trust user input
  if (!serviceName || !ALLOWED_SERVICE.has(serviceName)) {
    return res.status(400).json({ error: 'Service not allowed' });
  }

  try {
    // Use parameterized query to prevent SQL injection
    const result = await pool.query(
      'SELECT config FROM tenant_configs WHERE service_name = $1 AND tenant_id = $2',
      [serviceName, tenantId]
    );

    if (result.rows.length === 0) {
      return res.status(404).json({ error: 'Not found' });
    }

    res.json({ config: result.rows[0].config });
  } catch (err) {
    console.error(err);
    res.status(500).json({ error: 'Internal server error' });
  }
});

module.exports = app;

Example: Using DNS safely without zone transfer exposure

const dns = require('dns').promises;

// Only resolve internal, preapproved hostnames; do not reflect user input
async function resolveInternal(hostname) {
  const ALLOWED_INTERNAL = new Set(['internal-db.cockroachdb.local', 'node-internal.cockroachdb.local']);
  if (!ALLOWED_INTERNAL.has(hostname)) {
    throw new Error('Hostname not permitted');
  }
  return dns.resolve(hostname);
}

app.get('/api/internal-endpoints', async (req, res) => {
  const { hostname } = req.query;
  try {
    const addresses = await resolveInternal(hostname);
    res.json({ addresses });
  } catch (err) {
    res.status(400).json({ error: err.message });
  }
});

Operational practices

• Use environment variables for database connection strings and never log sensitive query parameters.
• Apply principle of least privilege to the CockroachDB user used by Express: grant only SELECT/INSERT/UPDATE needed for the feature, not administrative DNS or cluster controls.
• Leverage the middleBrick CLI to scan endpoints regularly with middlebrick scan <url> and review findings for BOLA/IDOR and Unsafe Consumption to ensure tenant isolation and input validation are effective.
• For continuous assurance, use the Pro plan to enable continuous monitoring and CI/CD integration so scans run on a schedule and builds can fail if risk scores degrade.