Fix BOLA (Broken Object Level Authorization) in Fresh
Broken Object Level Authorization (BOLA) remains the most critical vulnerability in modern Deno/Fresh applications. It occurs when a handler retrieves a resource based on a user-controlled ID without verifying if the authenticated user has the rights to access that specific object. In Fresh, this typically happens inside the Handlers defined in routes.
The Vulnerable Pattern
// routes/api/orders/[id].ts
export const handler: Handlers = {
async GET(_req, ctx) {
const { id } = ctx.params;
// VULNERABILITY: Directly fetching by ID from URL without checking ownerId
const order = await kv.get(["orders", id]);
if (!order.value) return new Response("Not Found", { status: 404 });
return Response.json(order.value);
}
};The Secure Implementation
To fix BOLA in Fresh, you must implement a strict policy of Identity-Based Access Control. First, ensure your route is protected by middleware that populates `ctx.state` with the authenticated user's identity. Second, never perform a lookup based solely on the URL parameter. You must query the database and then perform a server-side comparison between the resource's 'owner' attribute and the 'user.id' from your session state. If they do not match, return a 403 Forbidden to prevent cross-account data leakage.
// routes/api/orders/[id].ts export const handler: Handlers = { async GET(_req, ctx) { const { id } = ctx.params; const user = ctx.state.user; // Injected via auth middlewareif (!user) return new Response("Unauthorized", { status: 401 }); const order = await kv.get(["orders", id]); if (!order.value) return new Response("Not Found", { status: 404 }); // DEFENSE: Explicitly verify that the resource owner matches the session user if (order.value.userId !== user.id) { return new Response("Forbidden", { status: 403 }); } return Response.json(order.value);
} };
Your Fresh API
might be exposed to BOLA (Broken Object Level Authorization)
74% of Fresh apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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