Bola Idor in Chi (Go)

In the Chi framework for Go, Bola Idor refers to Broken Object Level Authorization, where an API endpoint fails to properly verify that the authenticated user is permitted to access a specific resource. When a Chi handler processes a request like /users/123/orders, the framework matches the URL to a route and invokes the corresponding handler. If the handler directly trusts the path parameter 123 without validating that the current user is authorized to view or modify that user's data, an attacker can manipulate the identifier to access another user's private information.

Consider the following minimal Chi route definition:

import (
    "net/http"
    "github.com/go-chi/chi/v5"
)

func main() {
    r := chi.NewRouter()
    r.Get("/users/{id}/orders", getOrdersHandler)
    http.ListenAndServe(":3000", r)
}

The handler might look like this:

func getOrdersHandler(w http.ResponseWriter, r *http.Request) {
    userID := chi.URLParam(r, "id")
    // Direct database query using the raw path parameter
    rows, _ := db.Query("SELECT * FROM orders WHERE user_id = ?", userID)
    // ... serialize and respond
}

Here, the application extracts the id from the URL path and uses it directly in a database query. There is no check that the authenticated principal (e.g., JWT claims, session data) matches id. An attacker who knows another user's ID can craft a request to /users/456/orders and retrieve that user's order history, even if they are not logged in as that user. This is a classic Bola Idor scenario in Chi: the framework's routing mechanism does not enforce authorization; it merely maps URLs to handlers.

Why does this happen in Chi? The framework encourages convention-over-configuration and provides flexible routing, but it does not automatically enforce per-resource permissions. Developers must explicitly validate ownership or role-based access before querying data. Without such checks, any endpoint that uses path parameters as resource identifiers becomes vulnerable to object-level authorization failures.

Real-world impact: In 2022, a major fintech API suffered a Bola Idor that exposed transaction histories of thousands of customers because the service used path parameters like /accounts/{account_id}/transactions without verifying that the caller had access to that account. The vulnerability was discovered via automated scanning, highlighting the importance of proactive testing.

To mitigate Bola Idor in Chi, developers must implement explicit authorization checks that compare the requested resource identifier with the authenticated user's identity or permissions. A typical remediation involves extracting the authenticated user's ID from the request context (e.g., JWT claims) and ensuring it matches the requested resource ID before proceeding.

Here is a concrete Go example using Chi and a middleware that enforces ownership:

import (
    "net/http"
    "github.com/go-chi/chi/v5"
    "github.com/golang-jwt/jwt/v5"
)

// authMiddleware extracts the user ID from the JWT token and stores it in the request context.
func authMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        token := r.Header.Get("Authorization")
        // Assume token parsing returns a *jwt.Token with "sub" claim as user ID
        claims := jwt.MapClaims{}
        _, err := jwt.ParseWithClaims(token, claims, func(t *jwt.Token) (interface{}, error) { return nil, nil })
        if err != nil {
            http.Error(w, "Unauthorized", http.StatusUnauthorized)
            return
        }
        userID := claims["sub"].(string)
        ctx := context.WithValue(r.Context(), "userID", userID)
        next.ServeHTTP(w, r.WithContext(ctx))
    })
}

// authorizeOrderAccess middleware checks that the requested order belongs to the authenticated user.
func authorizeOrderAccess(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        orderID := chi.URLParam(r, "id")
        userID := r.Context().Value("userID").(string)
        // Query the database to verify ownership
        var ownerID string
        err := db.QueryRow("SELECT user_id FROM orders WHERE order_id = ?", orderID).Scan(&ownerID)
        if err != nil {
            http.Error(w, "Order not found", http.StatusNotFound)
            return
        }
        if ownerID != userID {
            http.Error(w, "Forbidden", http.StatusForbidden)
            return
        }
        next.ServeHTTP(w, r)
    })
}

func getOrdersHandler(w http.ResponseWriter, r *http.Request) {
    // Retrieve user ID from context
    userID := r.Context().Value("userID").(string)
    orderID := chi.URLParam(r, "id")
    // At this point, authorizeOrderAccess has already validated ownership
    rows, _ := db.Query("SELECT * FROM orders WHERE order_id = ? AND user_id = ?", orderID, userID)
    // ... serialize and respond
}

func main() {
    r := chi.NewRouter()
    r.Use(authMiddleware)
    r.Group(func(router chi.Router) {
        router.Use(authorizeOrderAccess)
        router.Get("/users/{id}/orders/{orderID}", getOrdersHandler)
    })
    http.ListenAndServe(":3000", r)
}

In this pattern, the authorizeOrderAccess middleware performs a database lookup to confirm that the order belongs to the authenticated user before allowing the handler to execute. If the check fails, the request is rejected with a 403 Forbidden response. This approach ensures that even if an attacker manipulates the path parameter, the application will not expose unauthorized data.

Key takeaways for Go developers using Chi:

• Never trust path parameters for authorization; always verify ownership server-side.
• Use middleware to centralize authorization logic, keeping handlers focused on business logic.
• Leverage standard Go database drivers with parameterized queries to prevent injection while enforcing access control.

By integrating these checks into the request pipeline, you close the Bola Idor vector and align your API with the OWASP API Top 10 A01:2023 – Broken Access Control.