Credential Stuffing in Gorilla Mux

Credential stuffing in Gorilla Mux applications typically exploits predictable authentication patterns and missing rate limiting. Attackers use automated tools to test username/password combinations harvested from data breaches against your login endpoints.

The most common Gorilla Mux vulnerability occurs when developers use basic pattern matching without proper authentication controls. Consider this vulnerable pattern:

router := mux.NewRouter()
router.HandleFunc("/login", loginHandler).Methods("POST")
router.HandleFunc("/api/users/{id}", getUserHandler).Methods("GET")

Attackers can send thousands of POST requests to /login with different credentials. Without rate limiting middleware, Gorilla Mux will process each request, potentially allowing brute force attacks to succeed. The router's default behavior is to accept all valid HTTP methods for registered paths, making it trivial to flood authentication endpoints.

Another manifestation involves improper session management. Many Gorilla Mux applications use JWT tokens or session cookies without proper validation. An attacker who successfully logs in can reuse tokens indefinitely if expiration isn't enforced:

func loginHandler(w http.ResponseWriter, r *http.Request) {
    var creds Credentials
    json.NewDecoder(r.Body).Decode(&creds)
    
    user, err := authenticateUser(creds.Username, creds.Password)
    if err != nil {
        http.Error(w, "Unauthorized", 401)
        return
    }
    
    token := createToken(user) // No expiration set!
    w.Write([]byte(token))
}

Path traversal combined with credential stuffing creates additional risks. If your Gorilla Mux router uses variable extraction without validation:

router.HandleFunc("/api/users/{id}", getUserHandler).Methods("GET")

func getUserHandler(w http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)
    id := vars["id"]
    user, _ := db.GetUser(id) // No authentication check!
    json.NewEncoder(w).Encode(user)
}

An attacker who obtains valid credentials can enumerate user IDs and access any account. The router's path parameter extraction makes it easy to iterate through numeric IDs or common username patterns.

Detecting credential stuffing vulnerabilities in Gorilla Mux applications requires examining both the routing configuration and authentication middleware. Start by analyzing your router setup:

router := mux.NewRouter()

// Check for missing authentication middleware
router.HandleFunc("/admin", adminHandler).Methods("GET") // Vulnerable!
router.HandleFunc("/api/users/{id}", getUserHandler).Methods("GET") // Vulnerable!

middleBrick's black-box scanning can identify these vulnerabilities by testing authentication endpoints without credentials. The scanner sends multiple requests to login paths and analyzes response patterns. For Gorilla Mux applications, middleBrick specifically checks:

• Rate limiting absence on POST /login, /signin, /authenticate endpoints
• Missing authentication middleware on sensitive paths
• Predictable error messages that aid credential guessing
• Token generation without expiration or rotation

The scanner tests 12 security categories including authentication bypass attempts. For credential stuffing, it sends 100+ requests to authentication endpoints and analyzes success rates, response times, and error patterns.

Code analysis reveals router configuration issues. Look for these anti-patterns:

// Vulnerable: No authentication middleware
router.HandleFunc("/api/users/{id}", getUserHandler).Methods("GET")

// Vulnerable: Missing rate limiting
router.HandleFunc("/login", loginHandler).Methods("POST")

middleBrick's OpenAPI analysis can cross-reference your API specification with runtime findings. If your Swagger spec shows protected endpoints but middleBrick detects they're accessible without authentication, you have a configuration gap.

Runtime detection involves monitoring request patterns. Credential stuffing attacks show distinct signatures:

• High volume POST requests to authentication endpoints
• Consistent request rate (bots vs human patterns)
• Multiple failed attempts from same IP or user agent
• Credential rotation patterns (trying different username/password combinations)

middleBrick's scanner simulates these attack patterns to identify vulnerable endpoints before attackers do. The 5-15 second scan tests unauthenticated attack surfaces comprehensively.

Securing Gorilla Mux against credential stuffing requires implementing proper authentication middleware and rate limiting. Here's a comprehensive remediation approach:

package main

import (
    "github.com/gorilla/mux"
    "golang.org/x/time/rate"
    "net/http"
    "time"
)

type authMiddleware struct {
    limiter *rate.Limiter
}

func newAuthMiddleware() *authMiddleware {
    return &authMiddleware{
        limiter: rate.NewLimiter(rate.Every(5*time.Minute), 5), // 5 attempts per 5 minutes
    }
}

func (am *authMiddleware) limit(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        if !am.limiter.Allow() {
            http.Error(w, "Too many attempts", 429)
            return
        }
        next.ServeHTTP(w, r)
    })
}

func authRequired(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        token := r.Header.Get("Authorization")
        if token == "" || !validateToken(token) {
            http.Error(w, "Unauthorized", 401)
            return
        }
        next.ServeHTTP(w, r)
    })
}

func main() {
    router := mux.NewRouter()
    
    // Apply rate limiting to login endpoint
    loginRouter := router.PathPrefix("/login").Subrouter()
    loginRouter.Use(newAuthMiddleware().limit)
    loginRouter.HandleFunc("", loginHandler).Methods("POST")
    
    // Protect sensitive endpoints
    protectedRouter := router.PathPrefix("/api").Subrouter()
    protectedRouter.Use(authRequired)
    protectedRouter.HandleFunc("/users/{id}", getUserHandler).Methods("GET")
    protectedRouter.HandleFunc("/admin", adminHandler).Methods("GET")
    
    http.ListenAndServe(":8080", router)
}

Key remediation elements:

• Rate limiting middleware restricts authentication attempts (5 per 5 minutes)
• Authentication middleware protects all sensitive endpoints
• Subrouters organize protected vs public routes
• Consistent error responses prevent information leakage

Enhance token security with proper expiration and rotation:

func createSecureToken(user User) (string, error) {
    token := jwt.NewWithClaims(jwt.SigningMethodHS256, jwt.MapClaims{
        "user_id": user.ID,
        "exp": time.Now().Add(15 * time.Minute).Unix(), // 15 minute expiration
        "iat": time.Now().Unix(),
    })
    return token.SignedString([]byte("your-secret-key"))
}

func rotateToken(r *http.Request) (string, error) {
    // Implement token rotation to prevent reuse
    oldToken := r.Header.Get("Authorization")
    if oldToken != "" {
        // Invalidate old token and create new one
        return createSecureToken(getUserFromToken(oldToken))
    }
    return "", nil
}

Additional security measures:

// Implement account lockout after failed attempts
var failedAttempts = make(map[string]int)
var lastAttempt = make(map[string]time.Time)

func loginHandler(w http.ResponseWriter, r *http.Request) {
    var creds Credentials
    json.NewDecoder(r.Body).Decode(&creds)
    
    ip := r.RemoteAddr
    now := time.Now()
    
    // Check if lockout period active
    if last, exists := lastAttempt[ip]; exists {
        if now.Sub(last) < 15*time.Minute && failedAttempts[ip] > 5 {
            http.Error(w, "Account locked", 429)
            return
        }
    }
    
    user, err := authenticateUser(creds.Username, creds.Password)
    if err != nil {
        failedAttempts[ip]++
        lastAttempt[ip] = now
        http.Error(w, "Unauthorized", 401)
        return
    }
    
    // Reset counters on successful login
    delete(failedAttempts, ip)
    delete(lastAttempt, ip)
    
    token, _ := createSecureToken(user)
    w.Write([]byte(token))
}

middleBrick's Pro plan includes continuous monitoring that would detect if these protections fail in production. The scanner tests your authentication endpoints regularly and alerts you to new vulnerabilities.