Integrity Failures in Echo Go with Hmac Signatures

Integrity failures occur when a server does not adequately protect a message from tampering. In the Echo Go ecosystem, combining the framework’s flexible routing with Hmac Signatures used for request authentication can introduce subtle vulnerabilities if the signature is computed over an incomplete or mutable set of data. When designing a protected endpoint, developers must ensure that the Hmac covers all inputs that an attacker can influence, including query parameters, headers, and the request body. If any of these components are excluded from the signature, an attacker can modify the unprotected parts and forge a valid request without knowing the shared secret.

Echo Go applications often expose RESTful routes that accept JSON payloads and use middleware to validate Hmac Signatures before business logic executes. A common misconfiguration is to compute the Hmac only over the raw body bytes while ignoring headers such as X-Request-ID or authentication tokens passed in Authorization. Because the signature does not bind to these headers, an attacker can alter them to perform privilege escalation or inject replay metadata. Another vulnerability arises when the server normalizes inputs differently than the client, for example by reordering JSON keys or omitting null values before hashing. This inconsistency means that two semantically identical requests can produce different digests, allowing an attacker to submit a tampered request that the server mistakenly accepts as valid due to a mismatched canonicalization strategy.

In some cases, integrity failures intersect with IDOR or BOLA vulnerabilities. If the Hmac includes the resource identifier (such as a user ID in the URL path) but the server processes the request before verifying the identifier’s association with the caller, an attacker can iterate over identifiers while holding a valid signature. Because the signature is tied to the unverified identifier, the server may trust it and reveal or modify data belonging to other users. This pattern is particularly dangerous when the Hmac is computed over path parameters that are not validated against an access control model. The server may believe that the integrity of the request is intact, but the authorization boundary has been bypassed, leading to unauthorized read or write operations.

Real-world attack patterns mirror standard OWASP API Top 10 risks such as Broken Object Level Authorization and Tampering with Business Logic. For instance, an attacker could intercept a legitimate request, change the amount field in the JSON body, and attempt to recompute the Hmac. If the server excludes the body from the signature or uses a weak hash function, the tampered request may be accepted. Similarly, injection of additional headers or query parameters can alter processing logic, such as switching a transaction mode or changing the target of an operation. These scenarios highlight the importance of a strict, deterministic canonicalization process and comprehensive coverage of all mutable inputs when using Hmac Signatures in Echo Go services.

Remediation focuses on ensuring that the Hmac covers all data that an attacker can influence and that verification occurs before any business logic or data access. The server should define a canonical representation of the request before computing the digest. This includes selecting a consistent method for serializing JSON, sorting keys, and omitting or including optional fields in a documented way. In Echo Go, middleware can construct the signed string from the method, path, sorted query parameters, selected headers, and the raw body, then compare the computed Hmac to the one provided in a dedicated header using a constant-time comparison to avoid timing attacks.

Below is a concrete example of Hmac signature verification middleware for Echo Go. The middleware extracts a signature from the X-API-Signature header, builds a canonical string from the request components, and compares it with the Hmac computed using a shared secret. It rejects the request if the signatures do not match, preventing tampered inputs from proceeding.

package main

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

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

func HmacMiddleware(secret []byte) echo.MiddlewareFunc {
	return func(next echo.HandlerFunc) echo.HandlerFunc {
		return func(c echo.Context) error {
			// Build canonical components
			method := c.Request().Method
			path := c.Request().URL.Path
			query := c.Request().URL.Query()
			body := c.Request().Body // already read earlier if needed

			// Canonical query: sort keys and join key=value
			keys := make([]string, 0, len(query))
			for k := range query {
				keys = append(keys, k)
			}
			sort.Strings(keys)
			var qs []string
			for _, k := range keys {
				qs = append(qs, k+"="+query.Get(k))
			}
			canonicalQuery := strings.Join(qs, "&")

			// Canonical headers of interest
			contentType := c.Request().Header.Get("Content-Type")
			date := c.Request().Header.Get("Date")

			// Build canonical string
			canonical := method + "
" + path + "
" + canonicalQuery + "
" + contentType + "
" + date + "
" + string(body.([]byte))

			// Compute Hmac
			mac := hmac.New(sha256.New, secret)
			mac.Write([]byte(canonical))
			expected := hex.EncodeToString(mac.Sum(nil))

			// Provided signature
			provided := c.Request().Header.Get("X-API-Signature")
			if !hmac.Equal([]byte(expected), []byte(provided)) {
				return c.JSON(http.StatusUnauthorized, map[string]string{"error": "invalid signature"})
			}

			return next(c)
		}
	}
}

To complete the fix, ensure the client computes the signature using the exact same canonical string, including sorted query parameters and required headers. The server should also enforce that the Date header is within an acceptable window to prevent replay attacks, and that the Hmac uses a strong hash such as SHA-256. By validating the signature before accessing or modifying resources, the integrity of each request is preserved and the risk of tampering is significantly reduced.