Building an E2EE Chat App in Flask - Part 3: Keeping File Uploads Safe

A Flask end-to-end encrypted chat app added upload protections after unsafe files slipped through.

The app now whitelists allowed extensions, blocks suspicious or oversized uploads, and validates file types.

It also sanitizes filenames with Werkzeug’s secure_filename to prevent path traversal and dangerous names.

Approved uploads are stored in type-based folders to keep media handling organized and safer.