Session Fixation in Fiber

Remediating session fixation vulnerabilities in Fiber requires implementing proper session lifecycle management. The most critical fix is regenerating session IDs after authentication and privilege escalation events.

Here's the secure pattern for session management in Fiber:

package main

import (
    "github.com/gofiber/fiber/v2"
    "github.com/gofiber/fiber/v2/middleware/session"
)

func main() {
    app := fiber.New()
    
    // Secure session configuration
    store := session.New(session.Config{
        CookieSecure: true,    // Only send over HTTPS
        CookieSameSite: "Lax", // Prevent CSRF
        CookieHTTPOnly: true,  // Prevent JS access
        CookiePath: "/",       // Restrict path
    })
    
    app.Post("/login", func(c *fiber.Ctx) error {
        // Authenticate user first
        if !authenticate(c) {
            return c.SendStatus(fiber.StatusUnauthorized)
        }
        
        // CRITICAL: Regenerate session ID after auth
        sess, _ := store.Get(c)
        sess.ID() // Get current ID before destroying
        sess.Destroy()
        
        // Create new session with fresh ID
        newSess, _ := store.Get(c)
        newSess.Set("authenticated", true)
        newSess.Set("user_id", 123)
        newSess.Save()
        
        return c.SendStatus(fiber.StatusAccepted)
    })
    
    app.Listen(":3000")
}

func authenticate(c *fiber.Ctx) bool {
    // Your authentication logic here
    return true
}

The key security improvements in this code:

1. Session ID regeneration after successful authentication
2. Secure cookie configuration with Secure, SameSite, and HTTPOnly flags
3. Proper session destruction before creating a new one

For applications with role changes or privilege escalation, always regenerate sessions:

func promoteUser(c *fiber.Ctx) error {
    sess, _ := store.Get(c)
    
    // Check current privileges
    if sess.Get("role") != "admin" {
        // Regenerate session on privilege change
        sess.Destroy()
        newSess, _ := store.Get(c)
        newSess.Set("role", "admin")
        newSess.Save()
    }
    
    return c.SendStatus(fiber.StatusOK)
}

Additional Fiber-specific security measures include implementing session timeout and monitoring:

store := session.New(session.Config{
    Expiration:    time.Hour * 24, // 24-hour timeout
    GCInterval:    time.Minute * 30, // Cleanup interval
    CookieSecure:  true,
    CookieSameSite: "Lax",
})

// Middleware to check session validity
func sessionValidator(c *fiber.Ctx) error {
    sess, err := store.Get(c)
    if err != nil || !sess.Get("authenticated") {
        return c.SendStatus(fiber.StatusUnauthorized)
    }
    return c.Next()
}

By implementing these Fiber-specific session management patterns, you eliminate the session fixation attack surface while maintaining a secure user experience.