Fix BOLA (Broken Object Level Authorization) in Polka
BOLA (Broken Object Level Authorization) is the #1 API threat. In a minimalist framework like Polka, it's easy to fall into the trap of using route parameters directly in DB queries. If you trust the `:id` from the URL without verifying that the authenticated user actually owns that resource, you're leaking data. Attackers will simply increment IDs or spray UUIDs to scrape your entire backend.
The Vulnerable Pattern
const polka = require('polka'); const db = require('./db');polka() .get(‘/api/contract/:id’, async (req, res) => { // VULNERABLE: Direct reference to object ID without ownership validation // An attacker can change :id to any value to view other users’ contracts const contract = await db.Contracts.find(req.params.id);
if (!contract) { res.statusCode = 404; return res.end('Not Found'); } res.end(JSON.stringify(contract));
}) .listen(3000);
The Secure Implementation
To kill BOLA in Polka, stop treating the resource ID as the sole source of truth. The fix is 'Resource-Level Authorization'. Every time you hit the DB, your query must include a filter for the authenticated user's ID (`req.user.id`). If the user doesn't own the object, the DB returns null, and you return a 404. Never fetch an object first and check permissions later in the application logic if you can enforce it at the query level—this prevents race conditions and reduces the attack surface.
const polka = require('polka'); const db = require('./db'); const { auth } = require('./middleware');polka() .use(auth) // Middleware that populates req.user from JWT/Session .get(‘/api/contract/:id’, async (req, res) => { // SECURE: Query includes the owner_id constraint // This ensures the database only returns the record if it belongs to the requester const contract = await db.Contracts.findOne({ id: req.params.id, userId: req.user.id });
if (!contract) { // Use 404 to avoid revealing resource existence to unauthorized parties res.statusCode = 404; return res.end(JSON.stringify({ error: 'Contract not found' })); } res.end(JSON.stringify(contract));
}) .listen(3000);
Your Polka API
might be exposed to BOLA (Broken Object Level Authorization)
74% of Polka apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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