Token Replay in Buffalo (Go)

Token replay occurs when a valid authentication token is captured and maliciously reused to impersonate the original user. In a Buffalo application written in Go, this risk is amplified by how session and token handling is typically implemented. Buffalo uses secure cookies and optional token-based mechanisms (such as JSON Web Tokens for APIs), but if tokens lack strict per-request uniqueness or replay protection, an attacker who intercepts a token can reuse it within its validity window.

The combination of Buffalo’s convention-driven rapid development and Go’s low-level control can inadvertently encourage practices that do not adequately guard against replay. For example, developers might rely on JWTs with long expiration times, store tokens insecurely, or fail to bind tokens to a specific scope such as a nonce, timestamp, or client IP. Without mechanisms like one-time use, strict time windows, or cryptographic nonces, an intercepted token remains valid and can be replayed against unauthenticated endpoints.

Consider an API endpoint in Buffalo that accepts a bearer token in the Authorization header to authorize a sensitive action like transferring funds or changing an email address. If the endpoint only verifies the token’s signature and expiration, but does not ensure the token has not been used before, a captured token can be replayed from a different IP or at a later time. This maps to BOLA/IDOR and Authentication weaknesses identified in the 12 security checks, and may also intersect with Data Exposure if token leakage occurs in logs or error messages.

Real-world attack patterns include session fixation, where an attacker forces a user to use a known token, and token theft via insecure transport or XSS. Even with HTTPS, if tokens are not bound to a per-request context or if the API does not enforce rate limiting on token usage, replay becomes feasible. The scanner’s Authentication and BOLA/IDOR checks, alongside its LLM/AI Security probes, help detect endpoints where tokens lack replay safeguards by analyzing the unauthenticated attack surface and inspecting endpoint behaviors.

Because middleBrick scans APIs without agents or credentials, it can surface these risks by correlating spec definitions (OpenAPI 2.0/3.0/3.1 with full $ref resolution) against runtime responses. This helps teams identify endpoints that accept tokens but do not validate replay resistance, providing prioritized findings with severity ratings and remediation guidance mapped to frameworks like OWASP API Top 10 and PCI-DSS.

To mitigate token replay in Buffalo applications written in Go, implement per-request token uniqueness and strict validation. Below are concrete, idiomatic examples that demonstrate secure handling of bearer tokens and session cookies in a Buffalo app.

1. Use short-lived tokens with strict expiration and one-time-use tracking

Prefer short expiration times for JWTs and maintain a server-side cache of recently used token identifiers (e.g., JTI claims). This prevents reuse within the token’s lifetime.

package actions

import (
	"context"
	"time"

	"github.com/gobuffalo/buffalo"
	"github.com/gobuffalo/buffalo/middleware"
	"github.com/golang-jwt/jwt/v5"
)

var usedTokens = make(map[string]bool)

func ValidateToken(next buffalo.Handler) buffalo.Handler {
	return func(c buffalo.Context) error {
		auth := c.Request().Header.Get("Authorization")
		if auth == "" {
			return c.Render(401, r.JSON(map[string]string{"error": "authorization header required"}))
		}
		const bearerPrefix = "Bearer "
		if len(auth) < len(bearerPrefix) || auth[:len(bearerPrefix)] != bearerPrefix {
			return c.Render(401, r.JSON(map[string]string{"error": "invalid authorization format"}))
		}
		tokenString := auth[len(bearerPrefix):]

		// Parse and validate token
		token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
			// TODO: use your actual key function
			return []byte("your-secret-key"), nil
		})
		if err != nil || !token.Valid {
			return c.Render(401, r.JSON(map[string]string{"error": "invalid token"}))
		}

		// Check for replay using JTI claim
		if claims, ok := token.Claims.(jwt.MapClaims); ok {
			jti, ok := claims["jti"].(string)
			if !ok || jti == "" {
				return c.Render(401, r.JSON(map[string]string{"error": "missing token identifier"}))
			}
			if usedTokens[jti] {
				return c.Render(403, r.JSON(map[string]string{"error": "token already used"}))
			}
			usedTokens[jti] = true
			// Cleanup expired entries periodically (not shown)
		}

		// Attach claims to context for downstream use
		c.Set("claims", claims)
		return next(c)
	}
}

2. Bind tokens to contextual signals (nonce, timestamp, IP)

Include a nonce and timestamp in the token payload and validate them on each request. Also consider binding tokens to a client IP or user-agent to make replay across contexts harder.

package actions

import (
	"net"

	"github.com/gobuffalo/buffalo"
)

func ValidateTokenWithContext(next buffalo.Handler) buffalo.Handler {
	return func(c buffalo.Context) error {
		ip, _, _ := net.SplitHostPort(c.Request().RemoteAddr)
		// Assume claims are set by ValidateToken middleware
		claims := c.Get("claims").(jwt.MapClaims)
		if claims["ip"].(string) != ip {
			return c.Render(403, r.JSON(map[string]string{"error": "token context mismatch"}))
		}
		// Additional checks for nonce and timestamp can be added here
		return next(c)
	}
}

3. Secure cookie attributes for session-based authentication

If using Buffalo’s cookie-based sessions, enforce Secure, HttpOnly, SameSite, and a reasonable Expires/Max-Age to reduce exposure and opportunities for replay via stolen cookies.

package actions

import (
	"github.com/gobuffalo/buffalo"
	"github.com/gobuffalo/buffalo/middleware"
)

func App() *buffalo.App {
	app := buffalo.New(buffalo.Options{
		Env:         ENV,
		SessionStore: &middlebury.SessionStore{ /* options */ },
	})

	app.GET("/secure-endpoint", func(c buffalo.Context) error {
		// Ensure session cookies are set with secure attributes via middleware
		return c.Render(200, r.HTML("secure.html"))
	})

	// Configure session middleware with secure defaults
	app.Use(middleware.Session({ 
		Name:     "_app_session",
		Secure:   true,   // only over HTTPS
		HttpOnly: true,
		SameSite: http.SameSiteStrictMode,
		Expires:  time.Hour,
	}))
	return app
}

4. Combine with idempotency keys for critical operations

For sensitive actions, require an idempotency key in headers or body and store processed keys for a bounded window. This ensures that replaying the same request has no additional effect.

package actions

import (
	"sync"
	"time"

	"github.com/gobuffalo/buffalo"
)

var (
	idempotencyStore = make(map[string]time.Time)
	idempotencyLock  sync.Mutex
)

func IdempotencyMiddleware(next buffalo.Handler) buffalo.Handler {
	return func(c buffalo.Context) error {
		key := c.Request().Header.Get("Idempotency-Key")
		if key == "" {
			return c.Render(400, r.JSON(map[string]string{"error": "idempotency key required"}))
		}
		idempotencyLock.Lock()
		defer idempotencyLock.Unlock()
		if seen, ok := idempotencyStore[key]; ok && time.Since(seen) < 5*time.Minute {
			return c.Render(409, r.JSON(map[string]string{"error": "duplicate request"}))
		}
		idempotencyStore[key] = time.Now()
		// Optionally evict old entries in a real implementation
		return next(c)
	}
}

These Go-specific practices—short-lived tokens with JTI tracking, contextual binding, hardened cookies, and idempotency keys—directly address replay risks. When layered, they reduce the attack surface and align with the findings and remediation guidance that middleBrick provides through its scans, helping teams validate that replay protections are present and effective.