Missing Authentication in Echo Go with Hmac Signatures

When an Echo Go service uses Hmac Signatures for integrity but omits mandatory authentication checks on incoming requests, an attacker can bypass verification entirely. The vulnerability occurs when endpoints that should require authentication are left unguarded, allowing unauthenticated access to functionality that may still compute or verify Hmac headers.

In Echo Go, routes are typically defined without middleware that enforces authentication, and the developer may assume that Hmac validation alone is sufficient. For example, if a handler is registered without a required authentication middleware stack, any remote attacker can send crafted HTTP requests directly to the endpoint. Even when the service expects an Hmac signature in a header such as x-api-signature, the absence of authentication means the request is processed before signature checks are enforced or are inconsistently applied.

This misconfiguration maps to the BOLA/IDOR and Authentication categories in middleBrick’s 12 security checks. An unauthenticated attacker can invoke actions intended for authenticated users, such as reading or modifying resources, because Echo Go does not reject the request early. The presence of Hmac Signatures may create a false sense of security: the signature may be static, derived from a shared secret, or computed over a subset of the request that an attacker can replicate if they observe a valid pair of request and signature.

Consider an endpoint that updates a user profile. If the Echo Go route lacks authentication middleware and only validates the Hmac after parsing the body, an attacker can tamper with the user identifier in the payload while still providing a valid Hmac if the signing logic is weak or the secret is exposed. middleBrick’s unauthenticated scan would flag this as a high-severity finding because the endpoint exposes functionality without requiring proof of identity, and the Hmac mechanism does not compensate for missing authentication.

Real-world parallels include findings mapped to OWASP API Top 10:2023 — Broken Object Level Authorization and Missing Authentication. In PCI-DSS and SOC2 contexts, this combination fails controls around access control and auditability. middleBrick’s report would highlight the absence of enforced authentication before business logic, providing remediation guidance to introduce proper authentication and ensure Hmac verification is applied consistently to authenticated requests only.

To remediate, enforce authentication before Hmac validation in Echo Go, and ensure the signature is computed over a canonical representation of the request. Below are concrete patterns using middleware and handlers that demonstrate secure design.

1. Enforce authentication via middleware

Use Echo middleware to require a valid authentication token or session before reaching the Hmac verification step. This ensures no request bypasses identity checks.

func authMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
    return func(c echo.Context) error {
        token := c.Request().Header.Get("Authorization")
        if token == "" || !isValidToken(token) {
            return echo.NewHTTPError(http.StatusUnauthorized, "unauthorized")
        }
        return next(c)
    }
}

func isValidToken(token string) bool {
    // Implement your token validation logic (e.g., JWT verification)
    return len(token) > 0
}

2. Compute and verify Hmac over the full request

Sign the request body and selected headers to prevent tampering. Use a constant-time comparison to avoid timing attacks.

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

const sharedSecret = "your-secure-shared-secret"

func computeHmac(payload string) string {
    mac := hmac.New(sha256.New, []byte(sharedSecret))
    mac.Write([]byte(payload))
    return hex.EncodeToString(mac.Sum(nil))
}

func verifyHmac(r *http.Request, receivedSig string) bool {
    bodyBytes, err := io.ReadAll(r.Body)
    if err != nil {
        return false
    }
    // Restore body for downstream handlers
    r.Body = io.NopCloser(bytes.NewBuffer(bodyBytes))
    expected := computeHmac(string(bodyBytes))
    return hmac.Equal([]byte(expected), []byte(receivedSig))
}

3. Combine authentication and Hmac in a handler

Chain middleware so authentication runs first, then verify Hmac before processing business logic.

func secureHandler(c echo.Context) error {
    // Authentication already enforced by upstream middleware
    authToken := c.Get("user").(string) // set by auth middleware

    receivedSig := c.Request().Header.Get("x-api-signature")
    if !verifyHmac(c.Request(), receivedSig) {
        return echo.NewHTTPError(http.StatusBadRequest, "invalid signature")
    }

    var payload MyPayload
    if err := c.Bind(&payload); err != nil {
        return echo.NewHTTPError(http.StatusBadRequest, "invalid payload")
    }

    // Proceed with authenticated and verified request handling
    return c.JSON(http.StatusOK, map[string]string{"status": "ok", "user": authToken})
}

4. Route registration with middleware stack

Register routes in Echo with the proper order: authentication, Hmac validation, then business logic.

e := echo.New()
e.Use(authMiddleware)
e.POST("/profile", func(c echo.Context) error {
    // Hmac verification and handler logic
    return secureHandler(c)
})

By requiring authentication before Hmac verification, and by computing Hmac over the full request body and critical headers, you eliminate the gap where unauthenticated access is possible. This aligns with remediation guidance that middleBrick reports would provide, including mapping to OWASP API Top 10 controls and prioritizing fixes that enforce authentication at the edge.