Fix Business Logic Errors in Gatsby
Gatsby functions are the hidden underbelly of static sites. Developers often treat these serverless endpoints as lightweight helpers, ignoring the fact that they are full-blown Node.js environments. Business logic errors, specifically Insecure Direct Object References (IDOR) and broken access control, occur when you trust the client to provide identity or state. If your function updates a database based on a ID passed in the request body without verifying the session, you've just handed over the keys to your database.
The Vulnerable Pattern
export default async function handler(req, res) {
const { userId, bio } = req.body;
// VULNERABILITY: Trusting client-provided userId allows an attacker to update any user profile.
try {
const updatedUser = await db.user.update({
where: { id: userId },
data: { bio: bio }
});
res.status(200).json({ status: 'success', user: updatedUser });
} catch (err) {
res.status(500).json({ error: err.message });
}
}The Secure Implementation
The vulnerable snippet suffers from a classic IDOR. An attacker can intercept the request and change 'userId' to any other valid UUID to overwrite data. The secure implementation enforces business logic by ignoring the user-supplied identifier and instead extracting the 'userId' from a verified server-side session or JWT. Never trust data that identifies the 'who' or 'how much' when it comes from the client.
import { verifyToken } from '../lib/auth';export default async function handler(req, res) { const token = req.headers.authorization?.split(’ ’)[1]; const decoded = await verifyToken(token);
if (!decoded) { return res.status(401).json({ error: ‘Unauthorized’ }); }
const { bio } = req.body; // SECURE: Use the userId derived from the cryptographically signed JWT, not the request body. try { const updatedUser = await db.user.update({ where: { id: decoded.userId }, data: { bio: bio } }); res.status(200).json({ status: ‘success’, user: updatedUser }); } catch (err) { res.status(500).json({ error: ‘Internal Server Error’ }); } }
Your Gatsby API
might be exposed to Business Logic Errors
74% of Gatsby apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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