Why AI code editors generate insecure CORS middleware and how to fix it

Short summary

AI code editors like Cursor routinely generate CORS middleware that reflects the request Origin header back verbatim while allowing credentials, creating a CWE-942 vulnerability where any website can make authenticated calls to your API. This pattern persists in training data because it's the fastest fix that makes local CORS errors disappear. The fix is a hardcoded allowlist of trusted origins checked against each request, never reflecting what the browser sends.

• •AI editors generate origin-reflection CORS middleware that enables authenticated cross-site requests (CWE-942)
• •Pattern survives because it passes local testing across all dev ports and tools
• •Fix: explicit origin allowlist checked per-request, with separate dev and production lists

Generated with AI, which can make mistakes.