Token Replay in Buffalo

Token replay attacks in Buffalo applications occur when an attacker captures a valid session or authentication token (often a JWT or session ID) and reuses it to impersonate a legitimate user. This is particularly critical in Buffalo due to common patterns in its default authentication scaffolding and session management.

Buffalo frequently uses gorilla/sessions for cookie-based sessions or custom JWT middleware. A vulnerable pattern emerges when:

• Session tokens are not rotated upon privilege elevation: After a user logs in or escalates privileges (e.g., from user to admin), the same session token remains valid. An attacker who obtained the token earlier (via XSS, log leakage, or network sniffing) can replay it to gain elevated access.
• Logout does not invalidate the server-side session: Buffalo's default c.Destroy() or session clear operations might only delete the client-side cookie without server-side invalidation, allowing token reuse if the token was stolen before logout.
• Long-lived tokens without binding: JWTs with excessive expiration times and no binding to client properties (IP, User-Agent) are trivial to replay. Buffalo apps often set overly permissive MaxAge on session cookies.

Consider this vulnerable Buffalo handler that issues a session but fails to rotate it on subsequent sensitive actions:

// Vulnerable: Session ID remains constant after privilege change
func Login(c buffalo.Context) error {
    // Authenticate user...
    if err := c.WebSession().Put("user_id", user.ID); err != nil {
        return err
    }
    // No session regeneration here!
    return c.Redirect(302, "/dashboard")
}

func PromoteToAdmin(c buffalo.Context) error {
    // Check current user is allowed...
    // BAD: Reusing existing session without regeneration
    if err := c.WebSession().Put("role", "admin"); err != nil {
        return err
    }
    return c.Redirect(302, "/admin")
}

An attacker who steals the session cookie after the initial login (e.g., via XSS) can directly access the admin promotion endpoint because the session identifier never changed. This violates OWASP API Security Top 10 2023: B7: Identification and Authentication Failures and maps to PCI-DSS requirement 8.3 (session management).

Detecting token replay vulnerabilities in Buffalo requires examining both the application's session handling configuration and runtime behavior. Manual inspection should focus on:

• Session destruction logic: Verify that c.WebSession().Destroy() or equivalent is called on logout and that it invalidates the server-side session store (e.g., Redis, memory).
• Session regeneration: Check that c.WebSession().Renew() or a new session is created after login, privilege escalation, or sensitive operations.
• Cookie attributes: Ensure cookies have HttpOnly, Secure (in production), and appropriate MaxAge.
• JWT handling: If using JWTs, verify short expiration times (exp claim) and consider token binding or refresh token rotation.

Automated scanning with middleBrick provides a systematic approach. When you submit a Buffalo API endpoint (e.g., https://api.example.com/v1/users) to middleBrick, its unauthenticated black-box scan tests for token replay weaknesses through:

For example, middleBrick might:

1. Obtain a session token by logging in (if a login endpoint exists and is testable without credentials).
2. Trigger a logout via the Buffalo app's DELETE /session or similar.
3. Attempt to reuse the captured token on a protected endpoint (e.g., GET /profile).
4. If the request succeeds (HTTP 200), it flags a token replay vulnerability with high severity.

This aligns with CVE-2020-26116 (session fixation in Go's net/http cookie handling) and OWASP B7. middleBrick's report will show a per-category breakdown, highlighting the Authentication score drop and providing specific evidence like the reused token working post-logout.

To scan your Buffalo API:

# Using middleBrick CLI
middlebrick scan https://your-buffalo-api.com

The CLI returns a JSON report with a letter grade (A–F) and prioritized findings. In the Web Dashboard, you can track if your Authentication score improves after fixes.

Remediating token replay in Buffalo involves enforcing strict session lifecycle management. Use Buffalo's built-in session methods and secure defaults.

1. Regenerate Session on Privilege Change

Always call c.WebSession().Renew() after login, logout, or when a user's role changes. This generates a new session ID and invalidates the old one server-side.

// Secure: Regenerate session after login
func Login(c buffalo.Context) error {
    // Authenticate user...
    // Destroy old session if exists (e.g., from previous login)
    c.WebSession().Destroy(c)
    // Create a fresh session
    if err := c.WebSession().Renew(c); err != nil {
        return err
    }
    if err := c.WebSession().Put("user_id", user.ID); err != nil {
        return err
    }
    if err := c.WebSession().Put("role", user.Role); err != nil {
        return err
    }
    return c.Redirect(302, "/dashboard")
}

2. Proper Logout Invalidation

Ensure logout destroys both the client cookie and server-side session. Buffalo's Destroy does this when using server-side stores (like gorilla/sessions with a Redis backend). If using client-side JWTs, maintain a token blacklist.

// Secure: Full session destruction
func Logout(c buffalo.Context) error {
    // Invalidate server-side session
    c.WebSession().Destroy(c)
    // Clear cookie explicitly (Buffalo does this via Destroy, but be explicit if custom)
    c.WebSession().Options = &sessions.Options{
        MaxAge: -1, // Expire immediately
    }
    return c.Redirect(302, "/login")
}

3. Set Secure Cookie Attributes Globally

Configure session cookie options in your Buffalo app's init or middleware to enforce security:

// In your app's setup (e.g., NewApp)
func NewApp() *buffalo.App {
    app := buffalo.New(buffalo.Options{
        // ...
    })
    // Secure session cookie settings
    app.Use(SetSecureSessionCookie)
    return app
}

func SetSecureSessionCookie(next buffalo.Handler) buffalo.Handler {
    return func(c buffalo.Context) error {
        if c.WebSession() != nil {
            c.WebSession().Options = &sessions.Options{
                Path:     "/",
                MaxAge:   86400 * 7, // 1 week, adjust as needed
                HttpOnly: true,
                Secure:   app.Env == "production", // Only over HTTPS in prod
                SameSite: http.SameSiteStrictMode,
            }
        }
        return next(c)
    }
}

4. Short-Lived Tokens and Refresh Rotation

If using JWTs, set a short exp (e.g., 15 minutes) and implement refresh token rotation. Buffalo doesn't have built-in JWT support, but you can integrate libraries like golang-jwt/jwt with secure practices.

Verification with middleBrick: After applying these fixes, rescan your Buffalo API. The Authentication category score should improve, and the token replay finding should disappear. In the Pro plan, you can set CI/CD gates to fail builds if the score drops, preventing regression.

Remember: middleBrick detects and reports—it does not fix. Use its remediation guidance to harden your Buffalo application's session management against replay attacks.

• How does token replay specifically affect Buffalo applications?
  Buffalo apps often use gorilla/sessions with default settings that may not rotate session IDs on login or privilege changes. This allows an attacker who steals a session cookie (via XSS or network issues) to reuse it even after the user logs out or escalates privileges, leading to unauthorized access.
• Can middleBrick detect token replay in a Buffalo API that uses JWT instead of cookies?
  Yes. middleBrick's Authentication checks test for token invalidation and replay regardless of token format. For JWTs, it will attempt to capture a token (if login is testable) and reuse it after logout or expiration checks. It also flags long expiration times and lack of token binding as risk factors in its report.