File Upload Security Checklist for Node.js Production Rollouts

Most teams know the first few items on an upload-security checklist: file-size limits, maybe an extension allowlist, maybe a MIME check.

The gaps usually appear later, when the route reaches production traffic:

• A ZIP route has no archive policy.
• A suspicious document has no review path.
• Files reach object storage before the app decides whether to trust them.

Checklist

1. Limit the parser

Set byte limits, file-count limits, and route-specific constraints in the parser itself.

2. Keep untrusted bytes out of durable storage

Use memory-backed uploads for synchronous routes, or a quarantine bucket for direct-to-storage flows.

3. Use route-specific allowlists

Do not put archives, PDFs, SVGs, avatars, and mixed business documents behind one generic upload policy.

4. Validate content, not only metadata

Extensions and client MIME values are only the first filter.

5. Handle archives explicitly

Depth, total expansion, entry count, and traversal all need their own controls.

6. Decide what suspicious means

For some routes it means reject. For others it means quarantine and review.

7. Keep storage and serving paths safe

Non-executable, non-public by default. Signed delivery or controlled download endpoints where appropriate.

8. Log the verdict

Track verdicts, reasons, route, file size, and enough context to review trends later.

9. Test with real and safe test files

Use clean fixtures, borderline examples, archives, SVG, and safe malware-test patterns like EICAR.

10. Revisit the route when accepted file types change

The threat model changes whenever the route starts accepting new formats.

Where to go next

The concise docs version of this topic lives at Node.js file upload security checklist. For the broader route-design view, continue to Secure file uploads in Node.js: Beyond Extension and MIME Checks. From there, jump into the framework guides, the examples directory, or the GitHub repo.