The Access Control Bug Your AI Copilot Skips Every Time

TL;DR AI-generated API endpoints authenticate users but routinely forget ownership checks Any logged-in user can read, edit, or delete another user's data by guessing IDs One if statement is the difference between a secure API and a data breach I was doing a code review for a friend's SaaS a few weeks back. Invoice management app, small team, paying customers. The auth was solid. JWT tokens, proper middleware, refresh tokens done right. I was actually impressed until I hit the invoice endpoints. app . get ( ' /api/invoices/:id ' , authenticate , async ( req , res ) => { const invoice = await Invoice . findById ( req . params . id ); res . json ( invoice ); }); No ownership check. Any authenticated user could hit /api/invoices/1 , /api/invoices/2 , all the way up. Customer data, completely exposed to any other customer who figured out the pattern. The app had been live for three months. The dev built the whole backend with Cursor. Every endpoint had authentication middleware. None of th