Fix Business Logic Errors in Go Fiber
Business logic vulnerabilities in Go Fiber are logic-level bugs where the application's flow is subverted. Unlike memory safety issues, these are design flaws—think IDOR, race conditions, or parameter tampering that bypasses intended constraints. If you trust the client to tell you how much an item costs or which account they own, you've already lost. In Fiber, these usually manifest when developers lean too heavily on BodyParser without server-side validation of the state.
The Vulnerable Pattern
app.Post("/order", func(c *fiber.Ctx) error {
var order Order
// VULNERABILITY: Directly parsing client input into the model
if err := c.BodyParser(&order); err != nil {
return c.Status(400).SendString(err.Error())
}
// Attacker can send {"price": 0.01, "user_id": 1} even if they are user 99
return db.Create(&order).Error
})The Secure Implementation
The vulnerability lies in trusting the client as the source of truth for price and identity. The secure implementation uses a 'Strict Input Model' approach. First, it extracts the UserID from a secure session/JWT local, preventing IDOR. Second, it uses the client-provided ID only to look up the product in the database, pulling the price from a trusted source. Finally, it builds a new object explicitly rather than binding directly to a database model, preventing Mass Assignment attacks.
app.Post("/order", func(c *fiber.Ctx) error { // 1. Get authenticated user from context (e.g., from JWT middleware) authUser := c.Locals("user").(*User)var req struct { ProductID int `json:"product_id"` Quantity int `json:"quantity"` } if err := c.BodyParser(&req); err != nil { return c.Status(400).SendString("Invalid request format") } // 2. Fetch Source of Truth from Database var product Product if err := db.First(&product, req.ProductID).Error; err != nil { return c.Status(404).SendString("Product not found") } // 3. Construct the object server-side using trusted data newOrder := Order{ UserID: authUser.ID, // Enforce ownership ProductID: product.ID, Price: product.Price, // Use DB price, not client price Quantity: req.Quantity, } return db.Create(&newOrder).Error
})
Your Go Fiber API
might be exposed to Business Logic Errors
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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