Bola Idor in Buffalo with Jwt Tokens

Broken Object Level Authorization (BOLA) occurs when an API fails to enforce proper authorization checks between a subject (e.g., a user) and a resource identifier. In Buffalo, a common pattern is to use JWT tokens for identity, but relying only on the presence of a valid JWT without verifying scope or ownership can lead to BOLA. A JWT typically carries a subject claim (sub) and possibly roles or groups, but if the API exposes endpoints like /users/{id}/profile and only checks that a JWT is valid without ensuring that the {id} matches the sub in the token, an attacker can change the ID to access another user’s data.

Consider a Buffalo application that decodes a JWT to extract user information and then uses a numeric userID in the URL without cross-checking. For example, a request to /users/12345/profile with a valid JWT belonging to user 1001 can succeed if the server does not compare 12345 with the subject in the token. This is an authorization bypass, not an authentication failure, because the request is authenticated but not properly authorized. Buffalo routes often bind parameters directly to handler functions, making it easy to forget an ownership check. The risk is compounded when APIs also expose sensitive operations like changing email or password using identifiers that should be strictly scoped to the authenticated subject.

JWT tokens themselves do not prevent BOLA; they only provide identity. If token claims are not used to enforce object-level constraints, an attacker can iterate over IDs, UUIDs, or other references to discover or manipulate data. Common insecure patterns include using integer IDs without verifying they belong to the subject, failing to scope queries to the sub claim, or trusting path parameters without server-side validation. In Buffalo, developers might mistakenly assume that session-based protections or middleware that verifies JWTs are sufficient, but explicit checks comparing token claims to resource identifiers are required to mitigate BOLA.

Real-world attack patterns mirror this: an authenticated user modifies /accounts/{accountId}/transfer with a different accountId in the path while using their own JWT. If the server only validates the JWT signature and not that the accountId belongs to the user, the transfer occurs across accounts. This maps to OWASP API Top 10 A01:2023 broken object level authorization and can be discovered by scanners that compare authentication state with authorization decisions across object references.

To fix BOLA with JWT tokens in Buffalo, ensure that every handler that accesses a resource by an identifier validates that the identifier matches a claim in the token, typically the sub. Below are concrete code examples demonstrating secure patterns.

Example 1: Extract the subject from a JWT and compare it with the path parameter before proceeding.

// handlers/user_handler.go
package handlers

import (
  "context"
  "net/http"
  "strconv"

  "github.com/gobuffalo/buffalo"
  "github.com/gobuffalo/buffalo/middleware"
  "github.com/golang-jwt/jwt/v5"
)

func UserProfile(c buffalo.Context) error {
  // Assume JWT is validated by prior middleware and claims are set in context
  raw, ok := c.Get("claims")
  if !ok {
    return c.Error(http.StatusUnauthorized, errors.New("missing claims"))
  }
  claims, ok := raw.(jwt.MapClaims)
  if !ok {
    return c.Error(http.StatusUnauthorized, errors.New("invalid claims type"))
  }

  subject, ok := claims["sub"].(string)
  if !ok || subject == "" {
    return c.Error(http.StatusUnauthorized, errors.New("missing subject"))
  }

  idStr := c.Param("userID")
  if idStr == "" {
    return c.Error(http.StatusBadRequest, errors.New("userID is required"))
  }
  // If your user IDs are numeric, ensure they match the subject (which could be a UUID or numeric ID)
  if idStr != subject {
    return c.Error(http.StatusForbidden, errors.New("access denied to this resource"))
  }

  // Proceed to fetch user data safely, ensuring the ID matches the subject
  var user User
  if err := db.Where("id = ?", idStr).First(&user).Error; err != nil {
    return c.Error(http.StatusNotFound, errors.New("user not found"))
  }
  return c.Render(200, r.JSON(user))
}

Example 2: Scoped query using the subject claim to avoid ID-based enumeration.

// handlers/account_handler.go
package handlers

import (
  "context"
  "net/http"

  "github.com/gobuffalo/buffalo"
  "github.com/golang-jwt/jwt/v5"
)

func Transfer(c buffalo.Context) error {
  raw, ok := c.Get("claims")
  if !ok {
    return c.Error(http.StatusUnauthorized, errors.New("missing claims"))
  }
  claims, ok := raw.(jwt.MapClaims)
  if !ok {
    return c.Error(http.StatusUnauthorized, errors.New("invalid claims type"))
  }

  subject, ok := claims["sub"].(string)
  if !ok || subject == "" {
    return c.Error(http.StatusUnauthorized, errors.New("missing subject"))
  }

  accountID := c.Param("accountId")
  // Ensure the account belongs to the subject before proceeding
  var account Account
  if err := db.Where("id = ? AND user_id = ?", accountID, subject).First(&account).Error; err != nil {
    return c.Error(http.StatusForbidden, errors.New("account not accessible"))
  }

  // Perform transfer logic using the verified, scoped account
  // ...
  return c.Render(200, r.JSON(map[string]string{"status": "ok"}))
}

Additional remediation guidance includes: always scope database queries to the subject claim, avoid exposing internal IDs directly in URLs when possible or always verify ownership, and use consistent UUIDs rather than sequential integers to reduce enumeration risk. In Buffalo, leverage middleware to attach claims to the context and enforce a policy that every handler performing object-level access reconfirms the relationship between the subject and the requested resource.