Dns Cache Poisoning in Echo Go with Basic Auth

DNS cache poisoning (also known as DNS spoofing) occurs when an attacker injects forged DNS responses into a resolver’s cache, causing the resolver to return an attacker-controlled IP for a legitimate domain. In an API context, if an Echo Go service uses a hostname that is resolved via a shared or poisoned DNS cache, requests may be redirected to a malicious host. When Basic Auth is used, credentials are sent with every request; if those requests are redirected to an attacker, credentials can be harvested and the integrity of the API interaction is broken.

Echo Go is a popular HTTP router and framework for building Go services. Basic Auth in Echo Go is typically implemented via middleware that checks the Authorization header. When a vulnerable Echo Go application relies on DNS resolution for backend service calls (for example, calling an upstream API or a database host) and does not validate the resolved endpoint beyond the hostname, an attacker who can poison DNS may redirect traffic to a rogue server that terminates TLS with a valid certificate for the target hostname. Because the client sends Authorization headers to the resolved endpoint, the attacker gains access to those credentials or can manipulate the business logic by serving malicious responses that the client trusts.

The combination amplifies risk in two ways:

• The application may resolve a hostname once and cache it locally or rely on the operating system’s resolver cache. If DNS is poisoned after the initial resolution, subsequent requests continue to the malicious IP until the cache expires or the application re-resolves the hostname.
• Basic Auth credentials are included in each request. If the request is redirected to an attacker via DNS cache poisoning, credentials are exposed in clear text on the attacker’s server (even if the original scheme is HTTPS, the client may fail to validate the server’s identity if certificate pinning is not used).

Consider an Echo Go service that calls an internal user service via HTTP using a hostname like users.internal.example.com. If an attacker can poison DNS for that hostname, the Echo Go client may unknowingly send Basic Auth–protected requests to an attacker server. The attacker can then attempt to replay those credentials or modify upstream behavior based on the trusted context of the API call.

To reduce this class of issue, treat DNS as an untrusted network layer, avoid relying solely on DNS for security decisions, and enforce strict hostname verification and certificate validation on HTTP clients. Do not assume that a DNS name alone proves the identity of the endpoint.

Remediation focuses on preventing credential exposure and ensuring that the intended endpoint is reached even if DNS is manipulated. Use HTTPS with strict certificate validation, avoid sending credentials on unverified endpoints, and prefer safer credential mechanisms. Below are concrete code examples for an Echo Go client that calls an upstream service securely.

Insecure example to avoid: This example sends Basic Auth over HTTPS but does not verify the server certificate properly and relies on DNS without additional validation. If DNS is poisoned, credentials go to the attacker.

// Insecure: no custom TLS config, no hostname verification
package main

import (
	"net/http"
	"net/url"
	"github.com/labstack/echo/v4"
)

func main() {
	e := echo.New()
	reqURL := "https://users.internal.example.com/profile"

	req, _ := http.NewRequest(http.MethodGet, reqURL, nil)
	req.SetBasicAuth("alice", "secret123")

	client := &http.Client{} // No custom transport, no TLS verification control
	resp, _ := client.Do(req)
	defer resp.Body.Close()

	// Use resp...
}

Secure remediation: Use a custom HTTP client with TLS configuration that pins the server certificate or public key and validates the hostname explicitly. This ensures that even if DNS returns an attacker IP, the TLS handshake will fail unless the attacker presents the pinned certificate.

// Secure: custom transport with server name indication and optional cert pinning
package main

import (
	"crypto/tls"
	"crypto/x509"
	"net/http"
	"time"

	"github.com/labstack/echo/v4"
)

func newSecureClient() *http.Client {
	// Optionally load a pinned certificate(s)
	rootCAs := x509.NewCertPool()
	// pemData := []byte(`-----BEGIN CERTIFICATE-----
	// ...
	// -----END CERTIFICATE-----`)
	// rootCAs.AppendCertsFromPEM(pemData)

	// Enforce TLS 1.2+ and strong cipher suites
	tlsConfig := &tls.Config{
		MinVersion:               tls.VersionTLS12,
		ServerName:               "users.internal.example.com", // enforce SNI
		RootCAs:                  rootCAs,
		PreferServerCipherSuites: true,
		CipherSuites: []uint16{
			tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
		},
	}

	// Optionally pin a public key hash (SPKI pin) via VerifyPeerCertificate
	// tlsConfig.VerifyPeerCertificate = func(rawCerts [][]byte, verifiedChains [][]*x509.Certificate) error {
	// 	// compare pinned hash of leaf cert public key
	// 	return nil or error on mismatch
	// }

	transport := &http.Transport{
		TLSClientConfig: tlsConfig,
	}

	return &http.Client{
		Transport: transport,
		Timeout:   10 * time.Second,
	}
}

func main() {
	e := echo.New()
	reqURL := "https://users.internal.example.com/profile"

	req, _ := http.NewRequest(http.MethodGet, reqURL, nil)
	req.SetBasicAuth("alice", "secret123")

	client := newSecureClient()
	resp, _ := client.Do(req)
	defer resp.Body.Close()

	// Use resp...
}

Additional remediation guidance:

• Prefer token-based authentication (e.g., OAuth2 bearer tokens) over Basic Auth where possible; if Basic Auth is required, ensure it is only sent over mutually authenticated TLS.
• Use environment variables or a secrets manager for credentials, and avoid hardcoding usernames and passwords in source code.
• Consider using service meshes or sidecars to handle mTLS, reducing the need for application-side TLS complexity.
• In CI/CD, fail builds if security scans detect use of Basic Auth without strict TLS validation or if high-severity findings related to credential exposure appear.