Overview
Broken Object Property Level Authorization (BOLA) vulnerabilities arise when an API exposes parts of a resource (properties) without validating the caller's rights to access each property. This can lead to attackers viewing or mutating fields they should not have access to. A real-world analogue is CVE-2026-33745, where cpp-httplib forwarded stored Basic Auth, Bearer Token, and Digest credentials to arbitrary hosts during cross-origin redirects, enabling credential leakage if a malicious server redirected the client to an attacker-controlled host (CWE-200). While that CVE targets a C++ library, the underlying risk-trusting input or upstream behavior and leaking sensitive state across boundaries-maps to how per-property authorization can fail in Go (Gin). In a Go/Gin context, lacking granular checks on which fields of a resource a user may read or modify can expose secrets, ownership metadata, or other sensitive properties to unauthorized users. This guide ties the concept to Go-based services and shows concrete remediation.
Code Fix Example
Go (Gin) API Security Remediation
package main
import (
"net/http"
"strconv"
"github.com/gin-gonic/gin"
)
type Item struct {
ID int64 `json:"id"`
Name string `json:"name"`
OwnerID int64 `json:"owner_id"`
Secret string `json:"secret"` // sensitive property that should be hidden from non-owners
}
type ItemPublic struct {
ID int64 `json:"id"`
Name string `json:"name"`
}
type User struct {
ID int64
}
var items = map[int64]Item{
1: {ID: 1, Name: "Report", OwnerID: 42, Secret: "topsecret"},
2: {ID: 2, Name: "Invoice", OwnerID: 7, Secret: "baz"},
}
func main() {
r := gin.Default()
// Vulnerable pattern: exposes full Item including sensitive fields
r.GET("/vuln/items/:id", vulnerableGetItem)
// Fixed pattern: enforces ownership and returns sanitized view
r.GET("/fix/items/:id", fixedGetItem)
r.Run(":8080")
}
func getUserFromHeader(c *gin.Context) User {
switch c.GetHeader("X-User") {
case "42":
return User{ID: 42}
case "7":
return User{ID: 7}
default:
return User{ID: 0}
}
}
// Vulnerable handler: returns the full resource, including sensitive fields
func vulnerableGetItem(c *gin.Context) {
idParam := c.Param("id")
id, err := strconv.ParseInt(idParam, 10, 64)
if err != nil {
c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
return
}
item, ok := items[id]
if !ok {
c.JSON(http.StatusNotFound, gin.H{"error": "not found"})
return
}
// No authorization check on per-property access; all fields are returned
c.JSON(http.StatusOK, item)
}
// Fixed handler: enforces ownership and sanitizes response to expose only public fields
func fixedGetItem(c *gin.Context) {
idParam := c.Param("id")
id, err := strconv.ParseInt(idParam, 10, 64)
if err != nil {
c.JSON(http.StatusBadRequest, gin.H{"error": "invalid id"})
return
}
item, ok := items[id]
if !ok {
c.JSON(http.StatusNotFound, gin.H{"error": "not found"})
return
}
user := getUserFromHeader(c)
// Per-object authorization: ensure the caller owns the resource
if user.ID != item.OwnerID {
c.JSON(http.StatusForbidden, gin.H{"error": "forbidden"})
return
}
// Sanitize response to exclude sensitive fields
public := ItemPublic{ID: item.ID, Name: item.Name}
c.JSON(http.StatusOK, public)
}