Clickjacking in Fiber with Hmac Signatures

Clickjacking is a client-side attack where an attacker tricks a user into clicking or interacting with a hidden or disguised UI element inside an embedded frame (e.g., an iframe). When a Fiber application uses Hmac Signatures to validate requests but does not enforce frame-embedding protections, it can inadvertently expose endpoints to clickjacking. The Hmac mechanism ensures the request integrity and authenticity, but it does not prevent the browser from rendering the response inside a malicious page. An attacker can embed a protected endpoint in an invisible iframe and overlay interactive elements, causing the victim to perform unintended actions (such as changing settings or confirming transactions) while authenticated. Because the request includes a valid Hmac signature, the server treats it as legitimate. The presence of Hmac Signatures does not mitigate the need for anti-clickjacking defenses; instead, it highlights that integrity and authenticity controls operate at the request level, while clickjacking operates at the presentation and user-interaction level.

In a typical Fiber app using Hmac Signatures, the client includes a signature header generated with a shared secret and request metadata (method, path, timestamp, body). If the server responds with HTML that can be embedded, an attacker can frame that response and inject additional UI layers on top. For example, an endpoint that returns a confirmation form protected by Hmac can be loaded inside an attacker-controlled page, with buttons or links positioned to align with the embedded form’s action. When the user interacts, the forged click is paired with a valid Hmac-signed request, bypassing trust but not authorization checks. This is particularly risky for state-changing operations that rely solely on Hmac for integrity without additional anti-CSRF or framing controls. The attack does not require breaching the Hmac verification; it exploits the browser’s behavior in rendering framed content.

Fiber developers must recognize that Hmac Signatures protect against tampering, not social engineering or UI manipulation. Without explicit anti-clickjacking measures, endpoints using Hmac remain vulnerable to being framed. Attackers do not need to break the signature; they simply leverage the browser’s standard behavior to embed responses. This is why defense-in-depth is essential: Hmac Signatures should be combined with anti-frame headers and other UI-level protections to prevent clickjacking scenarios.

To remediate clickjacking risks in a Fiber application using Hmac Signatures, you should combine Hmac-based request validation with anti-frame defenses. Hmac ensures request integrity, but you must explicitly prevent the application’s responses from being embedded. Implement the following measures in your Fiber routes and middleware:

• Set anti-frame HTTP headers on all responses that could be targeted for clickjacking, especially those that render HTML or perform state-changing actions.
• Use consistent, strong Hmac signatures for sensitive operations, and ensure that the signature verification logic is applied before processing state-changing methods.
• Combine Hmac with CSRF tokens for state-changing endpoints, even when Hmac is used, to provide layered protection against both tampering and social engineering.

Below are concrete, working examples for a Fiber application that uses Hmac Signatures and includes anti-clickjacking headers.

Example 1: Hmac signature generation and verification with secure headers in Fiber.

// server.go
package main

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

	"github.com/gofiber/fiber/v2"
)

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

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

func verifyHmac(payload, receivedSig string) bool {
	expected := generateHmac(payload)
	return hmac.Equal([]byte(expected), []byte(receivedSig))
}

func main() {
	app := fiber.New()

	// Middleware to add anti-clickjacking headers
	app.Use(func(c *fiber.Ctx) error {
		c.Set("X-Frame-Options", "DENY")
		c.Set("Content-Security-Policy", "frame-ancestors 'none';")
		return c.Next()
	})

	app.Post("/transfer", func(c *fiber.Ctx) error {
		timestamp := c.Get("X-Timestamp")
		if timestamp == "" {
			return c.Status(fiber.StatusBadRequest).SendString("missing timestamp")
		}
		sig := c.Get("X-Signature")
		if sig == "" {
			return c.Status(fiber.StatusBadRequest).SendString("missing signature")
		}
		// Reconstruct payload as the client would
		payload := timestamp + c.Method() + c.Path()
		if !verifyHmac(payload, sig) {
			return c.Status(fiber.StatusUnauthorized).SendString("invalid signature")
		}
		// Process transfer safely
		return c.SendString("transfer initiated")
	})

	app.Listen(":3000")
}

Example 2: Client-side request construction including Hmac and safe headers.

// client.go
package main

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

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

func buildRequest() error {
	client := &http.Client{}
	timestamp := fmt.Sprintf("%d", time.Now().Unix())
	method := "POST"
	path := "/transfer"
	payload := timestamp + method + path

	h := hmac.New(sha256.New, []byte(sharedSecret))
	h.Write([]byte(payload))
	signature := hex.EncodeToString(h.Sum(nil))

	req, err := http.NewRequest(method, "http://localhost:3000"+path, strings.NewReader(`{}`))
	if err != nil {
		return err
	}
	req.Header.Set("X-Timestamp", timestamp)
	req.Header.Set("X-Signature", signature)
	req.Header.Set("X-Requested-With", "XMLHttpRequest")

	resp, err := client.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	// handle response
	return nil
}

These examples show how to generate and verify Hmac signatures in Fiber while also setting X-Frame-Options and Content-Security-Policy frame-ancestors to prevent framing. This combination addresses clickjacking without weakening the integrity guarantees provided by Hmac Signatures.