Insecure File Upload in Lovable App
Your Lovable app's file upload feature accepts any file type without validation, potentially allowing users to upload malicious scripts, executable files, or oversized files that could compromise your server or other users.
Without proper file validation, an attacker could upload a PHP script, an HTML file containing JavaScript, or a file disguised as an image that actually contains malware. If these files are served back to users, the malicious code could execute.
This is especially dangerous if uploaded files are stored in a publicly accessible location and served directly to users without content-type validation.
Error Messages You Might See
Common Causes
- No file type validation — The upload endpoint accepts any file regardless of extension or MIME type
- Client-side only validation — File type checks only happen in the browser, which can be easily bypassed
- No file size limits — Users can upload extremely large files, causing storage and bandwidth issues
- Files served with wrong content-type — Uploaded files are served back without proper Content-Type headers, allowing browser execution
- No malware scanning — Uploaded files are stored and served without any security scanning
How to Fix It
- Validate file types on the server — Check both file extension and MIME type on the backend, not just in the browser
- Set file size limits — Configure maximum upload sizes (e.g., 5MB for images, 25MB for documents)
- Rename uploaded files — Generate random filenames to prevent path traversal attacks
- Serve files with correct headers — Set Content-Type and Content-Disposition headers to prevent browser execution
- Use Supabase Storage policies — Configure bucket policies to restrict file types and sizes at the storage level
Real developers can help you.
Milan Surelia
Milan Surelia is a Mobile App Developer with 5+ years of experience crafting scalable, cross-platform apps at 7Span and Meticha. At 7Span, he engineers feature-rich Flutter apps with smooth performance and modern UI. As the Co-Founder of Meticha, he builds open-source tools and developer-focused products that solve real-world problems.
Expertise:
💡 Developing cross-platform apps using Flutter, Dart, and Jetpack Compose for Android, iOS, and Web.
🖋️ Sharing insights through technical writing, blogging, and open-source contributions.
🤝 Collaborating closely with designers, PMs, and developers to build seamless mobile experiences.
Notable Achievements:
🎯 Revamped the Vepaar app into Vepaar Store & CRM with a 2x performance boost and smoother UX.
🚀 Launched Compose101 — a Jetpack Compose starter kit to speed up Android development.
🌟 Open source contributions on Github & StackOverflow for Flutter & Dart
🎖️ Worked on improving app performance and user experience with smart solutions.
Milan is always happy to connect, work on new ideas, and explore the latest in technology.
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Get HelpFrequently Asked Questions
What file types should I allow?
Only allow the specific types your app needs. For profile pictures, allow only .jpg, .png, .webp. For documents, allow .pdf, .doc, .docx. Never allow .html, .js, .php, .exe, or .svg files from untrusted users.
Is Supabase Storage secure by default?
Supabase Storage requires you to set up bucket policies. By default, buckets are private, but you need to configure what file types and sizes are allowed, and who can upload.