Dns Cache Poisoning in Echo Go with Cockroachdb

DNS cache poisoning can affect an Echo Go service that uses CockroachDB when the application resolves database hostnames at runtime and caches the results in the Go standard library’s net.Resolver. If the resolver is not hardened, an attacker on the network can inject a malicious IP for the CockroachDB hostname, causing the Go service to direct SQL queries to a rogue server. Because CockroachDB typically serves SQL traffic over TCP/26257 and often uses TLS for encryption, the poisoned response may still succeed if the client skips verification or if the attacker relays traffic to a convincing proxy. This combination creates a supply-chain-like vector: the application trusts a single hostname resolution instead of using static connection parameters or strict certificate checks.

In an Echo Go API, routes that open a new database connection per request or reuse a sql.DB configured with a dynamic hostname are susceptible. For example, if the CockroachDB connection string is built from environment variables that resolve via DNS at startup and the process caches the IP, a poisoned cache entry can persist across restarts within the container lifecycle. The Echo Go middleware stack, which often includes logging, tracing, and middleware that depend on database calls, can inadvertently propagate tainted data if queries are forwarded to the malicious node. Data exposure and SSRF findings can appear in middleBrick scans when the resolver behavior allows external influence over connection targets.

Moreover, if TLS is used without strict hostname verification, a poisoned DNS entry pointing to a proxy that presents a valid certificate (e.g., from a compromised CA or a wildcard cert) can lead to credential theft or transaction manipulation. The 12 security checks in middleBrick, including Encryption and Data Exposure, are designed to surface such risks by correlating runtime behavior with spec definitions and flagging missing certificate checks or overly permissive network dialing patterns.

Remediation focuses on removing reliance on dynamic DNS at connection time, enforcing strict TLS verification, and avoiding mutable global state for resolution. Prefer static IPs or SRV records with a controlled resolver, and pin certificates. Below are concrete examples for an Echo Go service using CockroachDB.

1. Use static connection parameters and TCP with TLS

Instead of resolving a hostname at runtime, configure the connection string with a fixed IP or a load balancer that you control. Enforce TLS with custom root CAs and verify the server name.

package main

import (
	"crypto/tls"
	"crypto/x509"
	"database/sql"
	"fmt"
	"io/ioutil"
	"net"
	"net/http"

	"github.com/labstack/echo/v4"
	_ "github.com/lib/pq"
)

func newDB() (*sql.DB, error) {
	rootPEM, err := ioutil.ReadFile("/certs/ca.pem")
	if err != nil {
		return nil, err
	}
	rootCAs := x509.NewCertPool()
	if ok := rootCAs.AppendCertsFromPEM(rootPEM); !ok {
		return nil, fmt.Errorf("failed to parse root cert")
	}
	tlsConfig := &tls.Config{
		RootCAs:            rootCAs,
		ServerName:         "cockroachdb.example.com",
		InsecureSkipVerify: false,
	}
	connStr := "host=203.0.113.5 port=26257 user=appuser db=appdb sslmode=verify-full sslrootcert=/certs/ca.pem"
	db, err := sql.Open("postgres", connStr)
	if err != nil {
		return nil, err
	}
	db.SetConnMaxLifetime(0)
	return db, nil
}

2. Harden net.Resolver if dynamic resolution is required

If you must resolve hostnames at runtime (e.g., for multi-region clusters), replace the default resolver with one that uses a trusted DNS over HTTPS (DoH) server and disable caching of suspicious responses.

package main

import (
	"context"
	"net"
	"net/http"
	"time"

	"github.com/miekg/dns"
)

var resolver = &net.Resolver{
	PreferGo: true,
	Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
		d := &dns.Client{Timeout: 5 * time.Second}
		msg := dns.Msg{}
		msg.SetQuestion("cockroachdb.example.com.", dns.TypeA)
		in, _, err := d.Exchange(&msg, "1.1.1.1:53") // DoH upstream
		if err != nil {
			return nil, err
		}
		if in.Rcode != dns.RcodeSuccess {
			return nil, fmt.Errorf("dns error: %v", in.Rcode)
		}
		for _, a := range in.Answer {
			if a.Header().Rrtype == dns.TypeA {
				return net.DialIP(network, nil, a.(*dns.A).A)
			}
		}
		return nil, fmt.Errorf("no A record")
	},
}

func connectWithResolver(ctx context.Context) (*sql.DB, error) {
	host, err := resolver.LookupHost(ctx, "cockroachdb.example.com")
	if err != nil {
		return nil, err
	}
	connStr := fmt.Sprintf("host=%s port=26257 user=appuser dbname=appdb sslmode=require", host[0])
	return sql.Open("postgres", connStr)
}

3. Validate and restrict network scope

Use Echo Go middleware to reject requests that trigger unnecessary database connections and enforce allow-listed IP ranges for CockroachDB endpoints. This reduces the window for cache poisoning to affect runtime behavior.

func SecureMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		allowed := map[string]bool{"203.0.113.5:26257": true}
		host := c.Request().Header.Get("X-DB-Host")
		if host == "" || !allowed[host] {
			return c.String(http.StatusForbidden, "database endpoint not allowed")
		}
		return next(c)
	}
}

4. Apply middleBrick checks

Run middleBrick scans to surface Encryption and Data Exposure findings specific to your CockroachDB integration. The CLI can be used locally or in CI to validate that connection parameters and certificate verification align with best practices before deployment.

# Example CLI usage
middlebrick scan https://api.example.com/openapi.json