Dangling Dns in Grape with Cockroachdb

A dangling DNS record occurs when a hostname remains in DNS but the backing service or infrastructure has been decommissioned or reconfigured. In a Grape API that uses CockroachDB as its datastore, this situation can expose the application to data routing, trust, and injection risks.

Consider a Grape service that resolves a CockroachDB node via a CNAME or SRV record. If the backend cluster is scaled down, re-provisioned, or the environment is rebuilt without updating DNS, the API may continue to resolve to a stale address. During normal operation, the Ruby client (for example, cockroach-ruby or an ORM layer) opens TCP connections to the resolved host and port. If the stale DNS entry points to an unrelated service or a previously decommissioned node that has been re-issued to another tenant, the application may inadvertently connect to an unintended database instance.

This becomes particularly problematic when combined with CockroachDB’s multi-tenancy and network identity features. CockroachDB relies on node identity (node certificates and internal IDs) to enforce authentication and authorization. If the API connects to a different node that presents a valid certificate but belongs to another tenant or deployment, the API may trust the connection while the security perimeter has changed. Additionally, if the API embords connection parameters (such as hostnames) that are resolved at runtime, an attacker who can influence DNS (e.g., through a compromised resolver or cache poisoning) may redirect traffic to a malicious CockroachDB node that mimics the expected service. This can facilitate credential theft, data exfiltration, or insertion of malicious data into the API’s workflows.

From an API security perspective, a dangling DNS issue may not be apparent during development because the records appear valid. However, in production where infrastructure changes frequently, the mismatch between the API’s expected endpoint and the actual backend can lead to insecure defaults, such as skipping hostname verification or trusting any certificate presented. The 12 security checks in middleBrick, including Authentication and Data Exposure, would flag scenarios where unauthenticated or poorly authenticated access to a database endpoint is possible due to DNS misalignment, especially when combined with the API’s use of potentially untrusted external services.

To detect this class of risk, static analysis of configuration and runtime validation of resolved endpoints are useful. For example, ensuring that the CockroachDB connection host is either a fixed IP or a verified, short-lived DNS name, and that TLS certificates are validated against a pinned identity, reduces the window of misdirection. middleBrick’s OpenAPI/Swagger analysis can cross-reference declared server hosts with detected runtime behavior, highlighting mismatches when a declared hostname does not align with observed connections during the scan.

Remediation focuses on removing reliance on mutable DNS for security-critical connections, enforcing strict certificate validation, and ensuring that connection parameters are explicit and version-controlled.

First, avoid using dynamic DNS names that can change or be reused. Instead of resolving a hostname at runtime, pin the connection to a specific IP or a stable, short-lived certificate identity. In your Gemfile, use the pg gem (CockroachDB wire-compatible) and configure the host directly:

# config/database.yml or an environment-based initializer
production:
  url: postgresql://cockroach_user:[email protected]:26257/securebank?sslmode=verify-full&sslrootcert=/path/to/ca.pem

In the Grape API, load these settings explicitly and avoid merging runtime-resolved hostnames into the connection string:

# app.rb or an initializer
require 'bundler/setup'
require 'grape'
require 'pg'

module MyApi
  class App < Grape::API
    format :json

    helpers do
      def db_connection
        @db_connection ||= begin
          conn_url = ENV.fetch('COCKROACH_URL') # set from a secure source, not DNS
          conn = PG.connect(conn_url,
                            connect_timeout: 5,
                            sslmode: 'verify-full',
                            sslrootcert: ENV.fetch('COCKROACH_ROOT_CERT_PATH'))
          conn.exec('SHOW CLUSTER SETTING server.clock_offset_bound') # example liveness/test query
          conn
        end
      end
    end

    route_param :account_id do
      get :balance do
        row = db_connection.exec_params('SELECT balance FROM accounts WHERE id = $1', [params[:account_id]]).first
        { balance: row['balance'] } if row
      end
    end
  end
end

Second, enforce certificate pinning or at least strict hostname verification. If you must use DNS, ensure the client validates that the certificate’s Common Name or Subject Alternative Name matches an expected value and that the hostname matches the certificate. With CockroachDB, you can set a custom hostname in the certificate and verify it explicitly:

ssl_opts = {
  sslmode: 'verify-full',
  sslrootcert: '/path/to/ca.pem',
  sslcert: '/path/to/client.pem',
  sslkey: '/path/to/client.key',
  sslhostname: 'cockroachdb-prod.example.com' # enforce expected hostname
}
conn = PG.connect("host=#{ENV['COCKROACH_HOST']} port=26257 ssl=true", ssl_options: ssl_opts)

Third, implement runtime checks that validate the resolved endpoint against an allowlist. Before establishing a connection, compare the resolved IP or certificate fingerprint against a known set of values stored in your secure configuration:

require 'resolv'

expected_hosts = ['192.0.2.10', '192.0.2.11']
resolved = Resolv.getaddress(ENV['COCKROACH_HOSTNAME'])
raise 'Unexpected CockroachDB endpoint' unless expected_hosts.include?(resolved)

Finally, integrate these practices into your CI/CD and scanning workflows. Using the middleBrick CLI, you can scan your Grape endpoints to ensure declared server hosts align with runtime behavior. With the Pro plan, continuous monitoring will alert you if a scan detects mismatches or unauthenticated exposure that could indicate DNS or configuration drift. The GitHub Action can gate merges when security scores drop below your defined threshold, preventing deployments that rely on insecure or volatile DNS references.