Missing Tls in Echo Go with Hmac Signatures

Using Hmac Signatures in an Echo Go API without Transport Layer Security (TLS) exposes the signature and secret to network-level interception. When TLS is absent, all communication between client and server traverses the network in plaintext. An attacker on the same network or positioned between the client and server can observe HTTP requests, including headers that carry the Hmac signature.

Hmac Signatures typically rely on a shared secret to sign requests. The signature is often included in a header such as X-API-Signature. Without TLS, this header—and the secret used to generate it—is visible to anyone who can intercept the traffic. Even if the signature is not trivially reusable (because it includes a nonce or timestamp), exposing it can aid an attacker in conducting replay attacks or probing the service for weaknesses.

In Echo Go, if routes are defined without enforcing TLS, the framework serves traffic on HTTP as readily as HTTPS. For example, an unprotected route that expects an Hmac signature can be called over plain HTTP, allowing the signature to be captured. This becomes particularly problematic when the signature is tied to an API key or a secret that is static or long-lived, increasing the window for misuse. The combination therefore creates a scenario where the integrity mechanism (Hmac) is bypassed at the transport layer, undermining the assurance that the request has not been altered in transit.

Consider a scenario where a client computes an Hmac over the request payload and a timestamp, sending both in headers. Without TLS, an interceptor can see the timestamp and signature, and if the service does not enforce strict timestamp windows and one-time use, the interceptor may replay the request to the service while it is still valid. This illustrates how missing TLS turns a strong integrity check into a weak link, as the secret and the signed data are exposed.

To detect this specific risk, scanners perform unauthenticated checks that look for endpoints that accept sensitive operations over non-TLS channels and inspect whether integrity mechanisms like Hmac are used without adequate transport protection. The findings highlight the need to enforce HTTPS consistently and to treat Hmac signatures as protected credentials that must never traverse untrusted networks.

Remediation centers on enforcing HTTPS for all routes in Echo Go and ensuring that Hmac signature validation occurs only over secure channels. Below are concrete code examples that demonstrate a secure setup.

1. Enforce HTTPS with TLS configuration

Configure Echo to serve only over TLS by providing certificate and key files. This ensures that all traffic, including requests with Hmac signatures, is encrypted in transit.

// main.go
package main

import (
	"log"
	"net/http"

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

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

	// Define a protected route that requires Hmac signature validation
	e.POST("/webhook", func(c echo.Context) error {
		// Signature validation logic would go here
		return c.String(http.StatusOK, "ok")
	})

	// Enforce TLS with certificate and key files
	return e.StartTLS(":443", "cert.pem", "key.pem")
}

Using StartTLS ensures that the server listens only on HTTPS. For production, use valid certificates from a trusted CA and avoid self-signed certificates for public endpoints.

2. Hmac signature validation middleware over HTTPS

Implement middleware that validates the Hmac signature for incoming requests. This middleware should be applied to routes that handle sensitive operations and should only be active when serving over TLS.

// middleware/hmac.go
package middleware

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"net/http"
	"strings"

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

// VerifyHmac is a middleware that validates an Hmac signature in the X-API-Signature header
func VerifyHmac(secret string) echo.MiddlewareFunc {
	return func(next echo.HandlerFunc) echo.HandlerFunc {
		return func(c echo.Context) error {
			payload, err := c.Get("raw").([]byte)
			if err != nil {
				return c.String(http.StatusBadRequest, "invalid request body")
			}

			receivedSig := c.Request().Header.Get("X-API-Signature")
			if receivedSig == "" {
				return c.String(http.StatusUnauthorized, "missing signature")
			}

			mac := hmac.New(sha256.New, []byte(secret))
			mac.Write(payload)
			expectedSig := hex.EncodeToString(mac.Sum(nil))

			if !hmac.Equal([]byte(expectedSig), []byte(receivedSig)) {
				return c.String(http.StatusUnauthorized, "invalid signature")
			}

			return next(c)
		}
	}
}

Apply the middleware to routes that require integrity checks:

// main.go
package main

import (
	"log"
	"net/http"

	"github.com/labstack/echo/v4"
	"middlebrick-demo/middleware"
)

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

	// Apply Hmac validation middleware to the protected route
	e.POST("/webhook", middleware.VerifyHmac("your-256-bit-secret"), func(c echo.Context) error {
		return c.String(http.StatusOK, "webhook received")
	})

	// Enforce HTTPS in production
	return e.StartTLS(":443", "cert.pem", "key.pem")
}

3. Complementary protections

• Always use strong, randomly generated secrets for Hmac and rotate them periodically.
• Combine Hmac with other mechanisms such as short-lived timestamps or nonces to prevent replay attacks, even when TLS is enforced.
• Ensure that the service rejects requests with missing or malformed TLS client certificates if mutual TLS is used.

These steps ensure that Hmac Signatures in Echo Go are only validated over secure channels, mitigating the risk of exposure and maintaining the integrity of authenticated requests.