Arp Spoofing in Fiber (Go)

ARP spoofing (also called ARP poisoning) is a network-layer attack where an attacker sends falsified ARP messages over a local area network to associate their MAC address with the IP address of a legitimate device, such as a gateway or server. This enables man-in-the-middle (MITM) attacks, session hijacking, or denial of service. While ARP spoofing operates at Layer 2 of the OSI model, its impact on applications built with Go and the Fiber web framework is significant because Fiber, like any HTTP server, trusts the network path to clients. If an attacker successfully poisons the ARP cache of a Fiber server or its clients, they can intercept, modify, or redirect HTTP traffic—including API requests and responses—without the application’s knowledge.

Fiber, as a high-performance Go framework, does not include built-in protections against ARP spoofing because such attacks occur below the application layer. However, the combination of Fiber’s typical deployment patterns and Go’s networking behavior can exacerbate risk. For example, Fiber applications often run in containerized environments (e.g., Docker) or on virtual machines where ARP tables are managed by the host or orchestration layer. If these underlying networks are untrusted—such as in public cloud shared networks, development Wi-Fi, or compromised VLANs—an attacker on the same broadcast domain can poison ARP caches to redirect traffic meant for the Fiber server to their own machine.

Consider a scenario where a Fiber-based API handles sensitive operations like payment processing or user authentication. An attacker performing ARP spoofing could:

• Intercept unencrypted HTTP traffic to steal credentials or session tokens.
• Modify API responses in transit (e.g., altering JSON payloads to inject malicious commands).
• Redirect traffic to a phishing endpoint that mimics the legitimate API.
• Cause denial of service by associating the server’s IP with a non-existent MAC address.

Go’s net package, which Fiber uses under the hood, does not validate ARP bindings. The application assumes the IP-to-MAC mapping provided by the OS is correct. In environments where ARP is not secured (e.g., no dynamic ARP inspection on switches, no IPv6 neighbor discovery protections), this trust is misplaced. Furthermore, Fiber’s common use in microservices architectures increases the attack surface: inter-service communication often occurs over internal networks that may lack strict Layer 2 controls, making ARP spoofing a viable lateral movement technique after initial compromise.

It is critical to understand that middleBrick does not detect ARP spoofing directly, as it operates at the network layer and performs black-box API scanning from an external perspective. However, middleBrick can identify symptoms consistent with MITM attacks resulting from ARP spoofing, such as:

• Missing or weak encryption (flagged under the Encryption check).
• Exposure of sensitive data in responses (Data Exposure check).
• Successful injection attacks due to intercepted and modified requests (Input Validation check).
• Anomalous behavior in authentication flows (Authentication check).

By reporting these findings with remediation guidance, middleBrick helps teams identify potential compromises that may stem from lower-layer attacks like ARP spoofing, prompting investigation into network infrastructure security.

Since ARP spoofing is a Layer 2 attack, application-level code in Go and Fiber cannot prevent it directly. However, you can implement mitigations within your Fiber application to reduce the impact of successful ARP spoofing attempts by ensuring that even if traffic is intercepted, it cannot be read or tampered with. The primary defense is enforcing strong transport encryption and validating the integrity and authenticity of communications.

The most effective remediation is to enforce HTTPS with strict TLS configuration. Fiber supports TLS natively via the tls package. Below is a syntactically correct Go example showing how to configure a Fiber server to require HTTPS with modern TLS settings, which prevents attackers from decrypting or modifying intercepted traffic:

package main

import (
	"log"
	"github.com/gofiber/fiber/v2"
	"github.com/gofiber/fiber/v2/middleware/logger"
)

func main() {
	app := fiber.New(fiber.Config{
		DisableStartupMessage: true,
	})

	app.Use(logger.New())

	app.Get("/api/secure", func(c *fiber.Ctx) error {
		return c.JSON(fiber.Map{
			"message": "secure endpoint",
			"status":  "ok",
		})
	})

	// TLS configuration with modern cipher suites and versions
	cert := "cert.pem"
	key := "key.pem"

	log.Fatal(app.ListenTLS(":443", cert, key))
}

This code ensures all communication is encrypted. Even if an attacker performs ARP spoofing and intercepts packets, they cannot decrypt the TLS traffic without the server’s private key. To further harden the TLS configuration, you can customize the tls.Config:

package main

import (
	"crypto/tls"
	"log"
	"github.com/gofiber/fiber/v2"
)

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

	app.Get("/api/data", func(c *fiber.Ctx) error {
		return c.SendString("sensitive data")
	})

	// Custom TLS config enforcing TLS 1.2 or 1.3 and strong cipher suites
	tlsConfig := &tls.Config{
		MinVersion: tls.VersionTLS12,
		CipherSuites: []uint16{
			tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256,
			tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
			tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
		},
		PreferServerCipherSuites: true,
		SessionTicketsDisabled:  true, // mitigates ticket-based attacks
	}

	log.Fatal(app.ListenTLS(":443", "cert.pem", "key.pem", tlsConfig))
}

Additionally, implement HTTP Strict Transport Security (HSTS) to prevent downgrade attacks. Use Fiber’s middleware or add the header manually:

app.Use(func(c *fiber.Ctx) error {
	c.Set("Strict-Transport-Security", "max-age=31536000; includeSubDomains; preload")
	return c.Next()
})

For API clients communicating with your Fiber server, enforce certificate validation in Go to prevent accepting fraudulent certificates that an attacker might present after ARP spoofing and DNS manipulation:

package main

import (
	"crypto/tls"
	"fmt"
	"io"
	"net/http"
)

func main() {
	// Create HTTP client that validates server certificate
	client := &http.Client{
		Transport: &http.Transport{
			TLSClientConfig: &tls.Config{
				MinVersion: tls.VersionTLS12,
				// In production, use system roots; for custom CAs, append to pool
			},
		},
	}

	resp, err := client.Get("https://your-fiber-api.com/api/secure")
	if err != nil {
		fmt.Printf("request failed: %v\n", err)
		return
	}
	defer resp.Body.Close()

	body, _ := io.ReadAll(resp.Body)
	fmt.Printf("response: %s\n", body)
}

While these measures do not stop ARP spoofing at the network layer, they ensure that intercepted traffic remains confidential and integral. Combine them with network-level defenses such as dynamic ARP inspection (DAI) on switches, port security, and VLAN segmentation to address the root cause. middleBrick’s scan can validate that your Fiber API enforces HTTPS and has proper TLS configuration, providing actionable feedback if encryption is weak or missing—directly supporting your defense-in-depth strategy against ARP spoofing-related MITM risks.