Password Spraying in Chi

Password spraying in Chi applications typically exploits authentication endpoints that accept username/password combinations. Attackers leverage the framework's default authentication middleware to attempt common passwords across many accounts without triggering lockout mechanisms.

Chi's middleware package handles authentication state, but doesn't inherently protect against credential stuffing. A vulnerable Chi endpoint might look like:

func loginHandler(w http.ResponseWriter, r *http.Request) {
    var creds LoginCredentials
    if err := json.NewDecoder(r.Body).Decode(&creds); err != nil {
        http.Error(w, "Invalid request", http.StatusBadRequest)
        return
    }
    
    // No rate limiting, no account lockout
    user, err := authenticateUser(creds.Username, creds.Password)
    if err != nil {
        http.Error(w, "Invalid credentials", http.StatusUnauthorized)
        return
    }
    
    // Successful login
    w.WriteHeader(http.StatusOK)
}

The vulnerability emerges when attackers send requests like:

POST /login HTTP/1.1
Host: example.com
Content-Type: application/json

{"username":"admin","password":"password123"}

POST /login HTTP/1.1
Host: example.com
Content-Type: application/json

{"username":"user1","password":"password123"}

POST /login HTTP/1.1
Host: example.com
Content-Type: application/json

{"username":"user2","password":"password123"}

Chi's router middleware doesn't provide built-in rate limiting or authentication attempt tracking. Attackers can rotate through common passwords (Password123, Welcome1, Summer2023) across thousands of usernames, exploiting the fact that individual accounts never hit lockout thresholds.

API endpoints that use Chi's middleware.Auth without additional security controls are particularly vulnerable. The framework's stateless nature means each request is processed independently, making it easy to distribute password spraying attempts across multiple IP addresses or time intervals.

Detecting password spraying in Chi applications requires monitoring authentication patterns and implementing security scanning. middleBrick's black-box scanning approach is particularly effective for Chi APIs since it tests the unauthenticated attack surface without requiring access to source code.

Key detection patterns for Chi applications:

• Authentication endpoint monitoring - Track requests to /login, /authenticate, or custom auth routes
• Failed login rate analysis - Monitor authentication failure rates across different time windows
• Geographic distribution - Unusual login patterns from diverse geographic locations
• Credential rotation patterns - Multiple username attempts with identical password patterns

Using middleBrick to scan Chi APIs:

npx middlebrick scan https://api.example.com/login

The scanner tests for authentication weaknesses by attempting common password combinations across multiple simulated usernames. middleBrick's authentication category specifically checks for:

• Missing rate limiting on authentication endpoints
• Weak password policies allowing common passwords
• Lack of account lockout mechanisms
• Information leakage through error messages

For development teams, integrating middleBrick into CI/CD pipelines catches these issues before deployment:

name: Security Scan
on: [pull_request]

jobs:
  security:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Run middleBrick Scan
        run: |
          npx middlebrick scan https://staging.example.com/login --threshold B
        continue-on-error: true

The scanner's 12 security checks include authentication testing that specifically targets password spraying vulnerabilities common in Chi applications. Since Chi doesn't provide built-in authentication security, these external scans are critical for identifying weaknesses.

Securing Chi applications against password spraying requires implementing rate limiting, account lockout, and authentication monitoring using middleware and third-party libraries. Here's how to implement these protections:

Rate limiting middleware for Chi:

import (
    "time"
    "github.com/justinas/alice"
    "github.com/ulule/limiter/v3"
    "github.com/ulule/limiter/v3/drivers/middleware/stdlib"
    "github.com/ulule/limiter/v3/drivers/store/memory"
)

func setupRateLimiting() alice.Chain {
    rate := limiter.Rate{
        Limit: 5, // 5 requests per period
        Period: 1 * time.Minute,
    }
    
    store := memory.NewStore()
    limiterInstance := limiter.New(store, rate)
    middleware := stdlib.NewMiddleware(limiterInstance)
    
    return alice.New(middleware)
}

// Apply to authentication routes
router := chi.NewRouter()
router.With(setupRateLimiting()).Post("/login", loginHandler)

Account lockout implementation:

type authAttempt struct {
    Attempts int
    FirstAttempt time.Time
    LockedUntil  time.Time
}

var authAttempts = sync.Map{}

func checkLockout(username string) bool {
    if val, ok := authAttempts.Load(username); ok {
        attempt := val.(authAttempt)
        if time.Now().Before(attempt.LockedUntil) {
            return true // Account locked
        }
    }
    return false
}

func recordFailedAttempt(username string) {
    val, _ := authAttempts.LoadOrStore(username, authAttempt{})
    attempt := val.(authAttempt)
    
    if time.Since(attempt.FirstAttempt) > 5*time.Minute {
        attempt.Attempts = 1
        attempt.FirstAttempt = time.Now()
    } else {
        attempt.Attempts++
    }
    
    if attempt.Attempts >= 5 {
        attempt.LockedUntil = time.Now().Add(15 * time.Minute)
    }
    
    authAttempts.Store(username, attempt)
}

func loginHandler(w http.ResponseWriter, r *http.Request) {
    var creds LoginCredentials
    if err := json.NewDecoder(r.Body).Decode(&creds); err != nil {
        http.Error(w, "Invalid request", http.StatusBadRequest)
        return
    }
    
    if checkLockout(creds.Username) {
        http.Error(w, "Account temporarily locked", http.StatusTooManyRequests)
        return
    }
    
    user, err := authenticateUser(creds.Username, creds.Password)
    if err != nil {
        recordFailedAttempt(creds.Username)
        http.Error(w, "Invalid credentials", http.StatusUnauthorized)
        return
    }
    
    w.WriteHeader(http.StatusOK)
}

Enhanced authentication middleware:

func authMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // Check for suspicious patterns
        ip := r.RemoteAddr
        userAgent := r.Header.Get("User-Agent")
        
        // Log authentication attempts for monitoring
        logAuthenticationAttempt(ip, userAgent, r.URL.Path)
        
        next.ServeHTTP(w, r)
    })
}

func logAuthenticationAttempt(ip, userAgent, endpoint string) {
    // Integrate with monitoring system
    // Alert on unusual patterns (e.g., 100+ attempts from same IP)
}

Additional security measures for Chi applications:

• Implement CAPTCHA after multiple failed attempts
• Use IP-based rate limiting in addition to account-based limits
• Require multi-factor authentication for sensitive operations
• Log and monitor authentication patterns for anomaly detection

These Chi-specific implementations address the framework's lack of built-in authentication security while maintaining the clean, composable middleware pattern that makes Chi popular.