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.
Daniel Vázquez
Software Engineer with over 10 years of experience on Startups, Government, big tech industry & consulting.
hanson1014
Full-stack developer experienced in fixing and deploying AI-generated apps from Lovable, Bolt.new, Cursor, and Replit. I specialize in debugging Supabase integration issues (auth flows, RLS policies, database connections), fixing broken deployments, resolving routing/blank screen problems, and cleaning up messy React/Vite codebases. I also build production apps with the Claude API and have shipped a Mac desktop dev tool (Nexterm from scratch. Based in Hong Kong, fast turnaround.
Jen Jacobsen
I’m a Full-Stack Developer with over 10 years of experience building modern web and mobile applications. I enjoy working across the full product lifecycle — turning ideas into real, well-built products that are intuitive for users and scalable for businesses.
I particularly enjoy building mobile apps, modern web platforms, and solving complex technical problems in a way that keeps systems clean, reliable, and easy to maintain.
PawelPloszaj
I'm fronted developer with 10+ years of experience with big projects. I have small backend background too
Meïr Ankri
Full-stack developer specializing in React / Next.js / Node.js with 6+ years of experience. I've worked across various sectors including automotive (Reezocar/Société Générale), healthcare (Medical Link SaaS), and e-commerce (Glasman). I build web apps end-to-end, from architecture to production, with a focus on scalability, performance, and code quality. I also mentor junior developers and contribute to technical decisions and code reviews.
Jared Hasson
Full time lead founding dev at a cyber security saas startup, with 10 yoe and a bachelor's in CS. Building & debugging software products is what I've spent my time on for forever
Krishna Sai Kuncha
Experienced Professional Full stack Developer with 8+ years of experience across react, python, js, ts, golang and react-native. Developed inhouse websearch tooling for AI before websearch was solved : )
Dor Yaloz
SW engineer with 6+ years of experience,
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Supabase expert
Anthony Akpan
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Mehdi Ben Haddou
- Founder of Chessigma (1M+ users) & many small projects
- ex Founding Engineer @Uplane (YC F25)
- ex Software Engineer @Amazon and @Booking.com
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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.