Brute Force Attack in Gin (Go)

A brute force attack against a Gin service written in Go typically targets authentication endpoints by submitting a high volume of username and password combinations. Gin’s routing and middleware behavior can unintentionally aid an attacker when rate limiting is absent or misconfigured. Without explicit limits on login attempts, each account becomes a candidate for automated guessing. Attackers may use credential stuffing lists or generate guesses based on known password policies, leveraging Go’s efficient HTTP server performance to send many requests per second.

The Gin framework itself does not enforce authentication; it relies on developers to implement secure handlers and guards. If login routes do not enforce per-user or per-IP attempt tracking, there is no practical barrier to rapid guessing. Insecure account lockout policies, such as indefinite lockouts or lack of progressive delays, can make targeted brute force feasible. Additionally, verbose error messages help attackers distinguish between valid usernames and incorrect passwords, reducing the search space. When combined with weak password complexity requirements, the attack surface grows significantly.

Common insecure patterns include returning 200 OK with a generic message for both missing accounts and incorrect passwords, which removes feedback differentiation but does not stop high request volumes. Without proper instrumentation, you may not detect an ongoing attack until accounts are compromised. Because Gin does not include built-in brute force protection, developers must explicitly add throttling, progressive delays, and secure response handling to mitigate this risk.

To secure Gin endpoints against brute force, implement rate limiting and account lockout directly in Go handlers and middleware. Use a sliding window or token bucket approach with a concurrency-safe store such as a synchronized map or Redis-backed solution to track attempts per user and per IP. Ensure responses remain uniform regardless of account existence to avoid username enumeration.

Below is a minimal, production-style example using an in-memory store protected by sync.RWMutex. It limits login attempts per username and introduces progressive delays to slow down aggressive clients without locking accounts prematurely.

package main

import (
	"fmt"
	"net/http"
	"sync"
	"time"

	"github.com/gin-gonic/gin"
)

type attemptRecord struct {
	count     int
	firstSeen time.Time
}

type bruteForceGuard struct {
	sync.RWMutex
	attempts map[string]*attemptRecord
	maxAttempts int
	baseDelay   time.Duration
	maxDelay    time.Duration
}

func newBruteForceGuard(maxAttempts int, baseDelay, maxDelay time.Duration) *bruteForceGuard {
	return &bruteForceGuard{
		attempts:    make(map[string]*attemptRecord),
		maxAttempts: maxAttempts,
		baseDelay:   baseDelay,
		maxDelay:    maxDelay,
	}
}

func (g *bruteForceGuard) isAllowed(username string) bool {
	g.Lock()
	defer g.Unlock()

	record, exists := g.attempts[username]
	if !exists {
		g.attempts[username] = &attemptRecord{count: 1, firstSeen: time.Now()}
		return true
	}

	record.count++
	if record.count > g.maxAttempts {
		delay := g.baseDelay * time.Duration(record.count - g.maxAttempts)
		if delay > g.maxDelay {
			delay = g.maxDelay
		}
		time.Sleep(delay)
		return false
	}
	return true
}

func (g *bruteForceGuard) resetOnSuccess(username string) {
	g.Lock()
	defer g.Unlock()
	delete(g.attempts, username)
}

func loginHandler(guard *bruteForceGuard) gin.HandlerFunc {
	return func(c *gin.Context) {
		var req struct {
			Username string `json:"username" binding:"required"`
			Password string `json:"password" binding:"required"`
		}
		if err := c.ShouldBindJSON(&req); err != nil {
			c.JSON(http.StatusBadRequest, gin.H{"error": "invalid request"})
			return
		}

		if !guard.isAllowed(req.Username) {
			c.JSON(http.StatusTooManyRequests, gin.H{"error": "too many attempts"})
			return
		}

		// Replace with secure password verification
		valid := req.Username == "alice" && req.Password == "correct-hashed-password"
		if valid {
			guard.resetOnSuccess(req.Username)
			c.JSON(http.StatusOK, gin.H{"message": "authenticated"})
		} else {
			c.JSON(http.StatusUnauthorized, gin.H{"error": "invalid credentials"})
		}
	}
}

func main() {
	r := gin.Default()
	guard := newBruteForceGuard(5, 2*time.Second, 30*time.Second)
	r.POST("/login", loginHandler(guard))
	_ = r.Run(":8080")
}