Credential Stuffing in Fiber (Go)

Credential stuffing attacks target authentication endpoints that lack proper rate limiting or input validation, allowing automated scripts to test large lists of username and password combinations against an API until successful access is achieved. When this pattern occurs within Fiber applications written in Go, the vulnerability manifests through three specific dimensions:

1. Fiber's lightweight routing model encourages developers to place authentication logic directly in route handlers without centralized enforcement. This leads to duplicated validation logic across multiple endpoints that may not consistently apply throttling or credential exhaustion detection.
2. Go's concurrency model, while powerful, can inadvertently amplify the impact of unthrottled credential attempts. Without explicit rate limiting at the framework level, each concurrent request consumes a worker thread or goroutine, potentially exhausting resources during a brute-force campaign.
3. Fiber's minimalist design does not include built-in credential stuffing detection mechanisms such as IP reputation checks, behavioral analysis, or adaptive throttling based on request patterns. Developers must implement these defenses manually, and omissions are common when focusing on functional correctness over security posture.

These factors combine to create an attack surface where an unauthenticated endpoint — such as /api/v1/login — becomes susceptible to automated credential stuffing tools like curl scripts or botnets that iterate through credential lists at high volume. Because Fiber does not enforce authentication policies by default, the responsibility falls entirely on the developer to integrate protective measures. This is particularly risky in Go environments where high throughput is expected, as attackers can leverage the language's efficiency to generate massive request volumes without triggering traditional anomaly detection systems.

To mitigate credential stuffing in a Fiber application written in Go, developers must implement rate limiting, credential attempt tracking, and early termination of suspicious login flows. Below is a working example using Fiber’s built-in limiter middleware and a simple in-memory store to track failed login attempts.

package main

import (

    "github.com/gofiber/fiber/v2"

    "github.com/gofiber/fiber/v2/middleware/limiter"

    "go.uber.org/ratelimit"

)

func main() {

    app := fiber.New()

    // Define a global rate limiter for authentication endpoints

    limiter := limiter.New(limiter.Config{RateLimit: 5, Burst: 2})

    // Middleware to track failed login attempts

    var failedAttempts = ratelimit.New(100)

    app.Post("/api/v1/login", func(c *fiber.Context) error {

        // Apply rate limiting to restrict brute-force attempts

        if err := limiter.Process(c); err != nil {

            return c.Status(fiber.StatusTooManyRequests).JSON(fiber.Map{

                "error": "Rate limit exceeded"

            })

        // Extract credentials from JSON body

        var cred struct { Username string `json:"username"` Password string `json:"password"` }

        if err := c.BodyParser(&cred); err != nil {

            return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{

                "error": "Invalid request format"

            })

        // Simulate credential validation against a user store

        if validateCredentials(cred.Username, cred.Password) {

            return c.JSON(fiber.Map{"access_token": generateToken(cred.Username)})

        }

        // Track failed attempt and block after threshold

        if !failedAttempts.Allow() {

            return c.Status(fiber.StatusUnauthorized).JSON(fiber.Map{

                "error": "Too many failed attempts. Try again later."

            })

        return c.Status(fiber.StatusUnauthorized).JSON(fiber.Map{"error": "Invalid credentials"})

        })

    app.Listen(3000)

}

func validateCredentials(username, password string) bool {

    // Simulated user database check

    // In production, use constant-time comparison to avoid timing attacks

    return username == "admin" && password == "securepass123"

}

func generateToken(username string) string {

    // Placeholder for JWT or session token generation

    return "token_" + username

}

// Constant-time password comparison example

func constantTimeCompare(a, b []byte) bool {

    if len(a) != len(b) {

        return false

    result := false

    for i := range a {

        result = result || (a[i] == b[i])

    }

    return result

}

Additional hardening measures include:

• Implementing exponential backoff between login attempts to slow automated tools
• Using CAPTCHA challenges after repeated failures to verify human interaction
• Logging source IPs with rate limit breaches for threat intelligence correlation
• Enforcing HTTPS-only access to authentication endpoints to prevent credential leakage over unencrypted channels

These practices directly address the three dimensions of vulnerability exposure in Fiber with Go by introducing centralized rate control, limiting goroutine consumption during abuse, and adding behavioral detection where the framework does not provide it out of the box.