Insecure Direct Object Reference in Fiber with Jwt Tokens

Insecure Direct Object Reference (BOLA/IDOR) occurs when an API exposes internal object references—such as database IDs or sequential keys—and allows an authenticated user to access or modify data that belongs to another user. When using Jwt Tokens for authentication in a Fiber application, the vulnerability arises not from the token format itself, but from how the application uses identity information extracted from the token to authorize access to resources.

A typical pattern in Fiber is to authenticate requests by validating a Jwt Token and attaching the user’s claims (e.g., user ID) to the context. If endpoints then use user-supplied parameters—such as a path variable userID or a query parameter document_id—directly to look up and return data without verifying that the requested resource belongs to the authenticated subject, an IDOR is introduced. For example, a route like /users/:userID/profile might extract the token payload to identify the requester, but then blindly serve the profile for whatever :userID is provided in the URL. Because the token only confirms identity and not authorization for that specific target ID, an attacker can change the ID in the request and view or manipulate other users’ profiles.

Consider a route that fetches a document by ID without ensuring the document’s owner matches the authenticated subject extracted from the Jwt Token. If the token contains sub or a custom claim like user_id, and the handler uses that to identify the requester, but the database query is built from a request parameter without an ownership check, the endpoint leaks data horizontally across users. This is a classic BOLA/IDOR: the reference (document ID or user ID) is predictable or controllable, and authorization is incomplete because server-side ownership validation is missing.

In a microservices or frontend-driven application, this risk is compounded when APIs expose sequential or guessable IDs and rely solely on Jwt Tokens for access control. Tokens may contain roles or scopes, but if the API does not enforce that the subject can only act on their own resources, an attacker with a valid token can enumerate resources by iterating IDs and observing differences in response behavior or data. Proper authorization must bind the token’s identity to the resource’s ownership or shared access rules at the data layer, rather than trusting the client-supplied reference alone.

To remediate IDOR when using Jwt Tokens in Fiber, bind authorization decisions to the authenticated subject from the token and enforce ownership or access rules on every resource lookup. Never trust request parameters alone; always cross-check them against the identity derived from the validated Jwt Token.

Below are concrete, syntactically correct examples in Go using the gofiber/fiber package and a Jwt Token library such as golang-jwt/jwt. These examples demonstrate how to extract claims, perform server-side authorization, and avoid common pitfalls.

Example 1: User profile endpoint with proper ownership check

Ensure the requested user ID matches the subject in the Jwt Token.

c := fiber.New()

// Jwt Token validation middleware that sets user claims on context
func JWTMiddleware() fiber.Handler {
	return func(c *fiber.Ctx) error {
		auth := c.Get("Authorization")
		if auth == "" {
			return c.SendStatus(fiber.StatusUnauthorized)
		}
		tokenString := strings.TrimPrefix(auth, "Bearer ")
	token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
			if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
				return nil, fmt.Errorf("unexpected signing method")
			}
			return []byte(os.Getenv("JWT_SECRET")), nil
		})
		if err != nil || !token.Valid {
			return c.SendStatus(fiber.StatusUnauthorized)
		}
		if claims, ok := token.Claims.(jwt.MapClaims); ok && token.Valid {
			userID, _ := claims["user_id"].(string)
			c.Locals("userID", userID)
		}
		return c.Next()
	}
}

// Protected route: compare token subject with requested ID
c.Get("/users/:userID/profile", JWTMiddleware(), func(c *fiber.Ctx) error {
	requestedID := c.Params("userID")
	userID, ok := c.Locals("userID").(string)
	if !ok || userID == "" {
		return c.SendStatus(fiber.StatusUnauthorized)
	}
	if requestedID != userID {
		return c.Status(fiber.StatusForbidden).SendString("access denied")
	}
	// Fetch profile for userID from database
	var profile Profile
	if err := db.Where("id = ?", userID).First(&profile).Error; err != nil {
		return c.Status(fiber.StatusNotFound).SendString("not found")
	}
	return c.JSON(fiber.Map{"profile": profile})
})

This pattern ensures that even if an attacker changes :userID in the URL, the server compares it to the subject from the Jwt Token and denies access when they differ.

Example 2: Document access with role-based and ownership checks

For endpoints that involve relationships (e.g., documents owned by a user), validate both ownership and any required scopes or roles present in the token.

type Document struct {
	ID     uint   `gorm:"primaryKey"`
	UserID string `gorm:"index"`
	Title  string
	Data   string
}

c.Get("/documents/:documentID", JWTMiddleware(), func(c *fiber.Ctx) error {
	documentID := c.Params("documentID")
	userID, _ := c.Locals("userID").(string)

	var doc Document
	if err := db.Where("id = ? AND user_id = ?", documentID, userID).First(&doc).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return c.Status(fiber.StatusNotFound).SendString("document not found or access denied")
		}
		return c.SendStatus(fiber.StatusInternalServerError)
	}
	return c.JSON(fiber.Map{"document": doc})
})

By adding AND user_id = ? to the query, the database enforces authorization, preventing IDOR regardless of the document ID supplied. This approach aligns with the principle of server-side checks and avoids exposing internal references without proper context.

General guidance for Jwt Token usage in Fiber

• Always validate and parse Jwt Tokens before accessing protected resources.
• Extract identity (e.g., user_id) into request-local storage (context locals) and use it in all data-access queries.
• Never allow client-supplied identifiers to directly dictate which resource is returned without a server-side ownership or access-control check.
• Use parameterized queries to avoid injection and ensure ownership filters are applied consistently.
• If scopes or roles are encoded in the token, enforce them at the handler or middleware level to implement least privilege.

middleBrick can support this workflow by scanning your endpoints to detect missing ownership checks and improper use of Jwt Token claims, providing prioritized findings and remediation guidance to help you harden your API against BOLA/IDOR.