Xml External Entities in Restify with Cockroachdb

XML External Entity (XXE) injection occurs when an XML parser processes external entity references within untrusted XML data. In a Restify service that accepts XML payloads and interacts with Cockroachdb, this can lead to unauthorized data access, server-side request forgery (SSRF), or denial of service. The risk is realized when user-supplied XML is parsed without disabling external entity resolution, allowing an attacker to reference local files, internal services, or trigger unexpected network interactions that involve the Cockroachdb connection string or metadata.

Consider a scenario where a Restify endpoint accepts an XML document containing database identifiers or configuration overrides. If the XML parser resolves external entities, an attacker can supply an external DTD that references file:///etc/cockroachdb/certs/ca.pem or internal service endpoints used by Cockroachdb. This can disclose TLS certificates, service account tokens, or internal hostnames that inform network pivoting. When the Restify application later opens a Cockroachdb connection using those discovered details, the exposure becomes actionable.

The combination amplifies impact because Cockroachdb often runs in distributed clusters with strict network policies. An XXE vector may not directly alter data, but it can reveal connection parameters (hostnames, ports, node IDs) that help an attacker map the cluster topology. If the Restify service uses a shared Cockroachdb credential with broad permissions, discovered hostnames can be targeted for authentication bypass attempts or lateral movement. Even unauthenticated XXE probes can trigger outbound HTTP requests from the server (via entity expansion), hitting internal Cockroachdb HTTP status endpoints or gossip ports that are not exposed publicly.

Moreover, entity expansion (Billion Laughs) can consume server memory and CPU when parsing large, malicious XML documents. In a Restify deployment behind load balancers, this can degrade performance for Cockroachdb queries, causing timeouts or thread starvation. Because the parser performs network operations defined in the DTD, it can also probe internal IP ranges to validate whether hosts are reachable, effectively turning the Restify process into a network reconnaissance tool within the cluster’s security perimeter.

To illustrate the attack surface, an attacker might send the following crafted XML to a vulnerable Restify route expecting configuration data:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE foo [ <!ENTITY xxe SYSTEM "file:///opt/cockroachdb/cockroach.pem" >]>
<config><data>&xxe;</data></config>

If the Restify XML parser resolves &xxe;, the content of the PEM file may be returned in the response, potentially exposing certificates used by Cockroachdb. In environments where the same Restify instance also runs an HTTP client to communicate with Cockroachdb’s admin UI, SSRF via external entities can pivot to internal endpoints that only accept connections from localhost or service mesh IPs.

Because middleBrick tests unauthenticated attack surfaces, it can flag XXE findings in Restify endpoints that parse XML without disabling DTD loading. The scanner does not fix the parsing behavior but highlights how external references can expose backend systems like Cockroachdb and provides remediation guidance to harden the parser configuration.

Remediation centers on disabling external entity processing in the XML parser used by Restify and ensuring Cockroachdb credentials and endpoints are never inferred from untrusted input. Below are concrete, safe patterns for a Node.js Restify service.

1. Use a secure XML parser with DTD and external entity processing disabled.

Instead of the built-in xmldom parser (which resolves entities by default), prefer a parser that explicitly disables external entities. For example, using libxmljs with safe options or a streaming parser that ignores DOCTYPE declarations:

const xmlParser = require('fast-xml-parser');
const options = {
  ignoreAttributes: false,
  attributeNamePrefix: '',
  allowBooleanAttributes: false,
  parseNodeValue: true,
  parseAttributeValue: false,
  trimValues: true,
  // Reject DOCTYPE and external entities
  validation: false,
  forbidSynthetic: true
};

function parseXmlStrict(xmlString) {
  if (!xmlParser.validate(xmlString)) {
    throw new Error('Invalid XML');
  }
  return xmlParser.parse(xmlString, options);
}

app.post('/import', (req, res) => {
  try {
    const data = parseXmlStrict(req.body.toString());
    // Proceed with sanitized data; do not use XML-derived values for Cockroachdb credentials
    res.send(200, { ok: true });
  } catch (err) {
    res.send(400, { error: 'Invalid or unsafe XML' });
  }
});

2. Avoid constructing Cockroachdb connection strings from XML input.

Never map XML fields such as <host>, <port>, or <database> directly into Cockroachdb connection parameters. Instead, use environment variables or a secure secrets manager. If you must accept tenant-specific overrides, validate against a strict allowlist and use a dedicated Cockroachdb user with minimal privileges.

const { Cluster } = require('cockroachdb'); // hypothetical driver
const connectionString = process.env.COCKROACHDB_URL; // injected securely

async function queryWithSafeInput(tenantId, userInput) {
  // Validate tenantId against a denylist/allowlist
  if (!/^[a-z0-9-]+$/.test(tenantId)) {
    throw new Error('Invalid tenant identifier');
  }
  // Use parameterized queries to avoid injection
  const client = new Cluster({ connectionString });
  await client.connect();
  const result = await client.query('SELECT * FROM tenant_data WHERE tenant_id = $1', [tenantId]);
  await client.end();
  return result.rows;
}

3. Enforce network and schema-level protections.

Ensure the Restify service runs with network policies that restrict outbound connections to only Cockroachdb nodes on required ports. Combine this with Cockroachdb’s role-based access control so that the credentials used by Restify have read-only or write-only rights as needed, preventing privilege escalation via compromised application logic.

# Example connection options that avoid external discovery
const client = new Cluster({
  connectionString: 'postgresql://user:password@cockroachdb-internal:26257/dbname?sslmode=require',
  ssl: {
    ca: process.env.COCKROACH_CA // load from secure volume, not XML
  },
  max: 20,
  idleTimeout: 30000
});

By decoupling configuration from XML input and using strict parsers, Restify services can safely interact with Cockroachdb without introducing XXE or injection paths that expose cluster internals.