What causes wildcard CORS in Cursor?

AI models train on quick-start tutorials prioritizing 'it works' over security, so they default to `app.use(cors())` which sets origin *.

How do I secure Express CORS with env vars?

Split ALLOWED_ORIGINS in .env, validate origin in cors() callback, echo it back with credentials: true. Blocks everything else.

Is wildcard CORS a real security risk?

Yes—for auth APIs. Enables CSRF-like attacks where malicious sites steal session data via iframes or fetches on behalf of users.

🔒 Security & Privacy

Cursor's Wildcard CORS Blunder: 80% of AI-Generated Backends Are Vulnerable

Audited 25 Cursor projects last quarter: 20 had wildcard CORS in prod. That's not a bug—it's baked into AI training data, and it's handing attackers your users' sessions on a platter.

Open Source Beat Apr 11, 2026 3 min read

Code snippet showing Cursor-generated wildcard CORS config in Express app

⚡ Key Takeaways

Cursor defaults to wildcard CORS from flawed training data, exposing 80% of audited projects. 𝕏
Fix with env-var allowlists: explicit, auditable, prod-ready. 𝕏
Automate detection via semgrep—AI won't self-correct security sins. 𝕏

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#AI coding risks #CORS fix #CSRF prevention #Express.js security #cursor-ai #wildcard CORS

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Originally reported by Dev.to

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