Security for Vibe-Coded Marketplace Apps
Marketplaces connect buyers and sellers, handling payments between parties and managing trust. The multi-party nature creates unique security challenges around payment splitting, seller verification, and dispute handling.
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Why Security Matters for Marketplace Applications
Marketplaces are uniquely complex because you're handling money flow between multiple parties. Stripe Connect, PayPal for Marketplaces, and similar tools help, but AI-generated integration code often mishandles payment splits, refund logic, and seller payouts. Seller-side attacks are often overlooked. Malicious sellers can inject XSS through product listings, upload malicious files as product images, or exploit refund flows to get paid twice. Data isolation between sellers is also critical — one seller should never see another seller's revenue, customer list, or order details.
Security Risks
Payment flow manipulation
criticalAttackers modifying platform fees, seller payouts, or escrow release conditions through API manipulation.
Mitigation
Calculate all payment splits server-side. Never accept fee percentages or payout amounts from the client. Validate against your fee schedule in the database.
Seller data cross-contamination
highOne seller accessing another seller's orders, revenue data, or customer information.
Mitigation
Implement strict seller-scoped RLS policies. All queries must be filtered by the authenticated seller's ID at the database level.
Malicious product listings
highSellers injecting XSS or phishing content through product descriptions, images, or metadata.
Mitigation
Sanitize all seller-submitted content. Validate file uploads. Consider a content review queue for new sellers.
Security Checklist
Platform fees, seller payouts, and buyer totals all calculated on the server.
RLS policies ensuring sellers can only access their own orders and revenue data.
All seller-submitted HTML, images, and files validated and sanitized.
Verify Stripe Connect webhook signatures for payment events.
KYC process for sellers before they can receive payouts.
Automated limits on refunds with manual review for high-value disputes.
Real-World Scenario
A developer builds a freelancer marketplace using Lovable with Stripe Connect. The platform takes a 15% fee on each transaction. The fee percentage is sent from the frontend in the payment API call. A seller discovers this, sets up a buyer account, purchases their own service, and modifies the fee to 0% — pocketing the full amount. They repeat this with fake transactions to extract money from the platform.
Frequently Asked Questions
How do I secure payment splits in a marketplace?
Use Stripe Connect with server-side fee calculation. Store your fee schedule in the database, calculate the split on the server when creating the PaymentIntent, and never accept fee amounts from the client.
Should sellers be able to post HTML in listings?
Only with strict sanitization. Use an allowlist approach — permit specific safe tags (p, strong, em, ul, li) and strip everything else. Libraries like DOMPurify with a custom config work well for this.
How do I prevent sellers from seeing each other's data?
Implement RLS policies scoped to seller_id on all seller-related tables (orders, products, revenue, customers). Test by logging in as one seller and attempting to query another seller's data.
Security for Other Use Cases
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