Dns Cache Poisoning in Echo Go with Bearer Tokens

DNS cache poisoning can affect an Echo Go service that relies on external API calls identified by domain names. When the service resolves a domain to a malicious IP and then uses the resulting endpoint with Bearer Tokens, requests may be unintentionally sent to an attacker-controlled host. This can lead to token leakage if responses are intercepted or to token misuse if the poisoned endpoint echoes or logs Authorization headers.

In Echo Go, if hostname resolution is performed without strict validation of DNS responses, a poisoned cache entry may redirect traffic to an attacker server. Because Bearer Tokens are often passed via the Authorization header, an intercepted request can expose credentials to the attacker. This risk is particularly relevant when the service uses shared or long-lived tokens and does not enforce certificate pinning or strict transport-layer checks. An attacker who compromises DNS for a third‑party endpoint can observe or manipulate token‑bound requests, potentially gaining unauthorized access to protected resources.

Consider an Echo Go handler that calls a third‑party identity service to validate scopes. If the upstream IP for identity.example.com is poisoned, the handler may forward Bearer Tokens to an attacker server. Because the Authorization header is automatically included by HTTP clients when a base URL is configured, the tokens are exposed without additional code changes. The combination of a vulnerable resolver and token usage creates a chain where credential exposure follows successful poisoning, even if the application itself never mishandles the token string.

Remediation focuses on preventing unintended redirection and ensuring that Bearer Tokens are only sent to verified endpoints. Use strict hostname verification, avoid trusting potentially poisoned DNS by relying on well‑known service discovery or pinned endpoints, and ensure TLS is correctly validated. Below are concrete Echo Go patterns that reduce exposure.

Example 1: Explicit host verification with custom dialer

Override default resolution to validate the target host and use a custom transport that rejects mismatched certificates. This reduces reliance on system DNS cache for sensitive calls.

// main.go
package main

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

func main() {
	e := echo.New()

	// Custom dialer that enforces IP-to-hostname binding
	dialer := &net.Dialer{}
	tr := &http.Transport{
		TLSClientConfig: &tls.Config{
			InsecureSkipVerify: false, // always enforce verification
		},
		DialContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
			// Perform an additional check on the resolved address
			// For example, compare against an allowlist or use DNS-over-HTTPS
			return dialer.DialContext(ctx, network, addr)
		},
	}

	client := &http.Client{Transport: tr}

	e.GET("/call-external", func(c echo.Context) error {
		token := "valid_bearer_token_abc123"
		req, _ := http.NewRequest(http.MethodGet, "https://api.vendor.com/resource", nil)
		req.Header.Set("Authorization", "Bearer "+token)

		resp, err := client.Do(req)
		if err != nil {
			return c.String(http.StatusBadGateway, "upstream error")
		}
		defer resp.Body.Close()
		return c.JSONBlob(resp.StatusCode, nil)
	})

	e.Logger.Fatal(e.Start(":8080"))
}

Example 2: Avoiding automatic Authorization header leakage to unknown hosts

Ensure the HTTP client does not send Bearer Tokens to unexpected destinations by validating the final URL before execution. This pattern prevents accidental transmission to a poisoned endpoint after a cache‑poisoned redirect.

// middleware.go
package main

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

func SecureBearerMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		// Determine target host via a trusted configuration
		targetHost := "api.vendor.com"
		req := c.Request()
		if req.URL.Host != targetHost {
			return c.String(http.StatusForbidden, "host mismatch")
		}
		// Ensure token is only attached when host matches
		if !strings.HasPrefix(req.URL.Host, targetHost) {
			req.Header.Del("Authorization")
		}
		return next(c)
	}
}

// Usage in route
// e.Use(middleware.SecureBearerMiddleware)

Example 3: Enforcing HTTPS and certificate checks

Configure the HTTP client to require valid certificates and avoid insecure defaults. This prevents redirection to attacker‑controlled IPs served over HTTP after poisoning.

// client.go
package main

import (
	"crypto/tls"
	"crypto/x509"
	"net/http"
	"os"
)

func NewSecureClient() *http.Client {
	rootCAs := x509.NewCertPool()
	// Optionally load custom CA if needed
	// rootCAs.AppendCertsFromPEM([]byte(os.Getenv("CUSTOM_CA_PEM")))

	tlsConfig := &tls.Config{
		RootCAs:            rootCAs,
		InsecureSkipVerify: false,
	}

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

	return &http.Client{Transport: tr}
}