Fix Logic Flow Bypass in Go Fiber
Logic flow bypasses in Go Fiber typically manifest when developers rely on client-side state or fail to enforce strict state-machine transitions in middleware. If a user can jump from '/login' to '/admin/config' by skipping the '/mfa' or '/tos-accept' routes, your application logic is fundamentally broken. Secure Go Fiber apps must validate the specific state of a session, not just the existence of a session cookie.
The Vulnerable Pattern
package mainimport “github.com/gofiber/fiber/v2”
func main() { app := fiber.New()
// VULNERABILITY: This endpoint only checks if a user is 'logged_in'. // It does not verify if the user completed the mandatory MFA step. app.Get("/dashboard", func(c *fiber.Ctx) error { sessionID := c.Cookies("session_id") if sessionID == "" { return c.Status(401).SendString("Unauthorized") } return c.SendString("Welcome to the sensitive dashboard") }) app.Listen(":3000")
}
The Secure Implementation
To fix logic flow bypass, implement server-side state tracking using sessions. The fix involves three layers: 1. State Verification: Middleware must check for specific flags (e.g., 'mfa_passed') rather than general auth tokens. 2. Non-Linear Prevention: Ensure that reaching step N requires a cryptographically signed or server-stored flag from step N-1. 3. Explicit Deny: Default to a '403 Forbidden' if the required state sequence is not explicitly satisfied in the session store.
package mainimport ( “github.com/gofiber/fiber/v2” “github.com/gofiber/session/v2” )
var store = session.New()
func EnsureMFA(c *fiber.Ctx) error { sess, _ := store.Get(c) if sess.Get(“authenticated”) != true || sess.Get(“mfa_passed”) != true { return c.Status(403).JSON(fiber.Map{“error”: “Logic bypass detected: MFA required”}) } return c.Next() }
func main() { app := fiber.New()
// SECURE: Routes are protected by state-aware middleware app.Get("/dashboard", EnsureMFA, func(c *fiber.Ctx) error { return c.SendString("Welcome to the secure dashboard") }) app.Post("/mfa/verify", func(c *fiber.Ctx) error { // ... validation logic ... sess, _ := store.Get(c) sess.Set("mfa_passed", true) sess.Save() return c.SendString("MFA Verified") }) app.Listen(":3000")
}
Your Go Fiber API
might be exposed to Logic Flow Bypass
74% of Go Fiber apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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