Auth Bypass in Fiber (Go)

Auth bypass in a Fiber service built with Go typically occurs when access control is implemented at the application layer rather than being enforced by the framework or idiomatic patterns. Fiber is a fast, unopinionated web framework that does not enforce authentication or role-based checks by default. If routes are exposed without middleware that validates session tokens, JWTs, or other credentials, an attacker can invoke those endpoints directly.

In Go, developers sometimes mistakenly treat route registration as authorization, especially when using grouped routes without applying consistent middleware. For example, attaching handlers to app.Get("/admin", handler) without a preceding authentication middleware leaves the endpoint unguarded. Additionally, issues such as insecure cookie handling, missing secure flags, or improper parsing of authorization headers can lead to trusted identifiers being assumed rather than verified. The stateless nature of many Go-based Fiber APIs means that if token validation is skipped or conditional, a forged or missing token may be treated as valid.

Another vector specific to Go and Fiber involves improper handling of route parameters and type assertions. If an authorization check reads a user ID from the context and directly uses an interface value without type-safe assertion, an attacker may manipulate the parameter to escalate privileges or access another user’s resources (a BOLA/IDOR pattern). Because Go is statically typed, unchecked assertions can lead to runtime defaults that bypass intended restrictions.

Furthermore, middleware ordering matters in Fiber. If a developer registers public routes after protected routes, or fails to apply middleware globally using app.Use(), some paths may be unintentionally exposed. The framework’s flexibility allows multiple handler stacks, but without disciplined grouping and consistent middleware application, authentication boundaries become fragmented.

To mitigate auth bypass in Fiber with Go, enforce authentication via middleware and apply it consistently across protected routes. Below is a secure pattern using JWT validation middleware that checks the Authorization header before allowing access.

package main

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

func main() {
    app := fiber.New()

    jwtMiddleware := jwt.New(jwt.Config{
        SigningKey:   []byte("your-secret-key"),
        ContextKey:   "user",
        TokenLookup:  "header:Authorization",
        TokenPrefix:  "Bearer ",
        ErrorHandler: func(c *fiber.Ctx, err error) error {
            return c.Status(fiber.StatusUnauthorized).JSON(fiber.Map{
                "message": "Invalid or missing token",
            })
        },
    })

    // Protected route group
    protected := app.Group("/api")
    protected.Use(jwtMiddleware)
    {
        protected.Get("/admin", func(c *fiber.Ctx) error {
            user := c.Locals("user").(*jwt.Token)
            return c.JSON(fiber.Map{
                "message": "Admin access granted",
                "user_id": user.ID,
            })
        })

        protected.Get("/profile", func(c *fiber.Ctx) error {
            user := c.Locals("user").(*jwt.Token)
            return c.JSON(fiber.Map{
                "profile": user.ID,
            })
        })
    }

    // Public route
    app.Get("/health", func(c *fiber.Ctx) error {
        return c.SendString("OK")
    })

    app.Listen(":3000")
}

This approach ensures that every request to /api paths includes a valid JWT. The middleware extracts and validates the token, preventing unauthenticated access. For role-based checks, extend the middleware to inspect claims and reject insufficient privileges.

Apply middleware globally with app.Use(jwtMiddleware) if all routes require protection, or use grouped middleware for mixed public and private endpoints. Avoid relying on route ordering or assuming handlers are inherently protected. Always validate and assert types safely when reading user context to prevent BOLA/IDOR scenarios.

Use the CLI tool to verify your endpoints remain unguarded during development by running middlebrick scan <url>. In CI/CD, integrate the GitHub Action to fail builds if an endpoint’s risk score degrades, ensuring auth controls are continuously validated.