Bola Idor in Fiber with Jwt Tokens

BOLA (Broken Level of Authorization) / IDOR occurs when an API exposes user-specific resources without verifying that the requesting user is authorized to access them. In Fiber, this commonly arises when endpoints rely on JWT tokens for identity but then use user-supplied identifiers (e.g., a resource ID) to fetch or act on data without confirming ownership or permission. A typical vulnerable pattern is decoding the JWT to obtain a user identifier (such as user_id), then using a path or query parameter (like :id) to load a record without ensuring the record belongs to that user.

Consider a Fiber endpoint defined as GET /users/:id. If the handler decodes the JWT to obtain the authenticated user’s ID but then directly queries a database for the user with :id without comparing it to the authenticated user’s ID, the endpoint is IDOR. The JWT confirms identity but does not enforce authorization between resources. An attacker who can obtain or guess another user’s ID can read, modify, or delete that user’s data. This is BOLA/IDOR because the authorization check (does this user own this resource) is missing or incorrectly implemented.

JWT tokens themselves do not cause IDOR; the vulnerability emerges from how the server uses the claims in the token in combination with object references. For example, a token may contain sub and role, and the server may trust sub as the user ID. If the server uses this ID only for some operations (e.g., profile view) but fails to apply it consistently across endpoints that accept an :id parameter, the API surface becomes susceptible to IDOR. Inadequate use of scopes or roles within the token can also contribute when endpoints assume role-based access but do not validate object-level ownership.

Additional risk patterns include endpoints that accept an ID in the request body or query string and perform actions (like changing email or password) based on that ID while only validating the JWT. Because JWT validation typically confirms authentication, developers may incorrectly assume authorization is satisfied. Without explicit checks tying the resource to the user identity in the token, the endpoint exposes a BOLA/IDOR flaw. Even operations that appear benign—such as exporting or downloading a file referenced by an ID—can leak other users’ data if the ID is not scoped to the authenticated subject.

In real-world APIs, IDOR can also intersect with other checks performed by middleBrick. For instance, the scanner’s Authentication and BOLA/IDOR checks run in parallel and can surface cases where JWT usage is inconsistent across endpoints or where claims are not properly enforced at the resource level. Because middleBrick tests unauthenticated attack surfaces and then simulates authenticated scenarios (when tokens are provided), it can detect patterns where endpoints accept IDs without confirming they belong to the token’s subject, highlighting the need for object-level authorization in addition to token validation.

To remediate BOLA/IDOR in Fiber when using JWT tokens, ensure that every endpoint that accesses a user-specific resource enforces ownership by comparing the resource identifier to the subject (or other unique claim) from the validated token. Below are concrete, idiomatic examples in Go using the golang-jwt/jwt and github.com/gofiber/fiber/v2 packages.

1. Define claims and a JWT validation helper

Use a custom claims type and a helper that returns the user ID (subject) or an error. This centralizes validation and makes it easier to enforce consistent checks.

import (
	"github.com/gofiber/fiber/v2"
	"github.com/golang-jwt/jwt/v5"
)

type CustomClaims struct {
	UserID string `json:"user_id"`
	jwt.RegisteredClaims
}

func parseToken(c *fiber.Ctx) (string, error) {
	auth := c.Get("Authorization")
	if auth == "" {
		return "", fiber.ErrUnauthorized
	}
	// Bearer 
	tokenString := auth[7:]
	token, err := jwt.ParseWithClaims(tokenString, &CustomClaims{}, func(token *jwt.Token) (interface{}, error) {
		// TODO: use your actual key; for HMAC, use []byte("your-secret")
		return []byte("your-secret"), nil
	})
	if err != nil || !token.Valid {
		return "", fiber.ErrUnauthorized
	}
	claims, ok := token.Claims.(*CustomClaims)
	if !ok {
		return "", fiber.ErrUnauthorized
	}
	return claims.UserID, nil
}

2. Enforce ownership in a route handler

In the handler for a user-specific resource, first obtain the authenticated user ID, then load the requested resource and compare IDs. If they do not match, reject with 403.

func GetUserProfile(c *fiber.Ctx) error {
	userID, err := parseToken(c)
	if err != nil {
		return err
	}

	// :id comes from the route, e.g., GET /users/:id
	requestedID := c.Params("id")
	if requestedID == "" {
		return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{"error": "missing user id"})
	}

	// TODO: replace with your actual data access layer
	var profile UserProfile
	if err := db.Where("id = ?", requestedID).First(&profile).Error; err != nil {
		return c.Status(fiber.StatusNotFound).JSON(fiber.Map{"error": "not found"})
	}

	// Critical authorization check: ensure the profile belongs to the authenticated user
	if profile.UserID != userID {
		return c.Status(fiber.StatusForbidden).JSON(fiber.Map{"error": "access denied"})
	}

	return c.JSON(profile)
}

3. Apply the same check for write operations

For endpoints that modify or delete a resource, repeat the ownership verification before performing the action. Avoid relying on the caller-supplied ID alone to decide which resource to act upon.

func UpdateUserEmail(c *fiber.Ctx) error {
	userID, err := parseToken(c)
	if err != nil {
		return err
	}

	requestedID := c.Params("id")
	if requestedID == "" {
		return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{"error": "missing user id"})
	}

	// Ensure the resource exists and belongs to the user before updating
	var existing UserProfile
	if err := db.Where("id = ?", requestedID).First(&existing).Error; err != nil {
		return c.Status(fiber.StatusNotFound).JSON(fiber.Map{"error": "not found"})
	}
	if existing.UserID != userID {
		return c.Status(fiber.StatusForbidden).JSON(fiber.Map{"error": "access denied"})
	}

	var payload struct {
		Email string `json:"email" validate:"email"`
	}
	if err := c.BodyParser(&payload); err != nil {
		return c.Status(fiber.StatusBadRequest).JSON(fiber.Map{"error": "invalid payload"})
	}

	// Proceed with update
	existing.Email = payload.Email
	db.Save(&existing)
	return c.JSON(existing)
}

4. Use middleware for common authorization patterns

You can create a Fiber middleware that enforces that a resource ID matches the token subject for selected routes, reducing duplication and ensuring consistent checks across handlers.

func RequireResourceOwnership() fiber.Handler {
	return func(c *fiber.Ctx) error {
		userID, err := parseToken(c)
		if err != nil {
			return err
		}
		// Expect the route to define a param named "id"
		if c.Params("id") == "" {
			return c.Next()
		}
		// This example assumes a context key or a subsequent handler will validate ownership.
		// You can also perform DB checks here if you have a loader function.
		c.Locals("authenticated_user_id", userID)
		return c.Next()
	}
}

// Then in route setup:
// app.Get("/users/:id", RequireResourceOwnership(), GetUserProfile)

These examples emphasize that JWT tokens provide identity, but servers must still enforce object-level authorization by comparing the token’s subject to the resource identifier on every sensitive operation. Combining validated JWT claims with explicit ownership checks in each handler (or shared middleware) effectively mitigates BOLA/IDOR in Fiber APIs.