Dangling Dns in Express with Cockroachdb

A dangling DNS configuration in an Express application that uses CockroachDB can expose runtime behavior that reveals internal infrastructure and supports SSRF or enumeration attacks. CockroachDB typically communicates via service names or DNS records in clustered deployments; if those records are incomplete, unresolved, or point to internal namespaces, an attacker may be able to infer environment topology or trigger resolution paths that leak information.

When an Express API connects to CockroachDB using a hostname that does not resolve correctly in the deployment environment, the application may still attempt to open connections. During a middleBrick scan, unauthenticated checks for SSRF and Input Validation probe how the runtime handles these resolution failures. An endpoint that dynamically builds a CockroachDB connection string from user-controlled input—such as a tenant identifier or subdomain—can inadvertently allow an attacker to supply a hostname that resolves to internal services. Because middleBrick tests the unauthenticated attack surface, it can detect whether DNS-based SSRF paths exist when a malicious hostname forces connections toward internal CockroachDB nodes or other internal endpoints.

Additionally, inconsistent DNS resolution across environments (development, staging, production) can cause the application to log resolution errors or stack traces. These logs may disclose internal hostnames, cluster IDs, or network zones, which an attacker can correlate with reconnaissance data. The LLM/AI Security checks in middleBrick specifically look for system prompt leakage and output patterns that could expose such details; while not directly testing logs, the scan flags endpoints that reflect internal errors or metadata. A misconfigured DNS search suffix or an incomplete SRV record for CockroachDB can therefore turn a simple configuration oversight into an information disclosure vector that compounds SSRF, BOLA/IDOR, or unsafe consumption risks.

In practice, this means an Express route that accepts a cluster identifier and builds a CockroachDB URI without strict validation can become a pivot point. middleBrick’s Inventory Management and Unsafe Consumption checks examine whether the API safely handles unexpected or malicious inputs that could redirect database connections. If the hostname supplied by an attacker is not strictly constrained, the scan may identify the endpoint as high risk due to potential SSRF or excessive agency patterns where the application attempts to interact with unintended network services.

middleBrick reports such findings with severity and remediation guidance, mapping them to frameworks like OWASP API Top 10 and noting related checks such as SSRF, Input Validation, and LLM/AI Security. Because the scanner runs in 5–15 seconds without credentials, teams can quickly identify whether their Express+Cockroachdb surface exposes dangling DNS paths before deploying changes.

Remediation focuses on strict input validation, controlled DNS usage, and avoiding dynamic hostname assembly from untrusted data. Ensure that any connection parameters for CockroachDB are fixed at build time or sourced from a secure configuration store, and that user input never directly specifies hostnames or ports used for database connections.

Use environment variables for connection details and validate them at startup. For example, define a fixed connection string in your deployment environment and read it in Express without concatenating user-controlled segments:

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

// DO NOT build connection strings from user input
const pool = new Pool({
  connectionString: process.env.COCKROACHDB_URL,
  ssl: {
    rejectUnauthorized: true
  }
});

app.get('/tenant-data', async (req, res) => {
  try {
    const result = await pool.query('SELECT id, name FROM tenants WHERE id = $1', [req.user.tenantId]);
    res.json(result.rows);
  } catch (err) {
    res.status(500).json({ error: 'Internal server error' });
  }
});

If you must support multi-tenant routing, map tenant identifiers to fixed connection pools or use row-level security instead of altering the hostname:

const pools = {
  alpha: new Pool({ connectionString: process.env.COCKROACHDB_ALPHA_URL, ssl: { rejectUnauthorized: true } }),
  beta: new Pool({ connectionString: process.env.COCKROACHDB_BETA_URL, ssl: { rejectUnauthorized: true } })
};

app.get('/data/:tenant', async (req, res) => {
  const pool = pools[req.params.tenant];
  if (!pool) {
    return res.status(400).json({ error: 'Invalid tenant' });
  }
  try {
    const result = await pool.query('SELECT * FROM accounts WHERE tenant_id = $1', [req.user.id]);
    res.json(result.rows);
  } catch (err) {
    res.status(500).json({ error: 'Internal server error' });
  }
});

For CockroachDB-specific drivers that support SRV records, pin the expected service name and do not allow client-supplied hostnames to override it. Configure your DNS and Kubernetes service references so that resolution is stable and points only to authorized endpoints. middleBrick’s OpenAPI/Swagger analysis can validate that your API schema does not expose parameters that influence database connection targets, and the CLI can be used in CI/CD to enforce these rules before deployment.

Finally, ensure that error handling does not surface raw connection or DNS resolution messages. Use generic error responses and structured logging that redacts internal hostnames. With these fixes, the Express+Cockroachdb stack avoids dangling DNS risks while remaining compatible with secure deployment patterns.