🚨 Critical Security Vulnerability: RLS Policy Breach

Summary

The current Row Level Security (RLS) policies contain a critical vulnerability that allows any anonymous user to access ALL other anonymous users' spending data, completely breaking user data isolation.

Vulnerability Details

Root Cause

The RLS policies use a wildcard pattern user_id LIKE 'anon_%' that matches ALL anonymous users instead of isolating individual users:

CREATE POLICY "Users can view own spending entries" ON public.spending_entries
    FOR SELECT USING (user_id = current_setting('request.jwt.claims', true)::json->>'sub' OR user_id LIKE 'anon_%');

Impact Assessment

• Severity: 🔴 CRITICAL
• Data Exposure: Complete cross-user data access for anonymous users
• Affected Tables: spending_entries, categories
• User Impact: ALL anonymous users can see each other's spending data

Proof of Concept

1. Anonymous User A gets ID: anon_abc123
2. Anonymous User B gets ID: anon_xyz789
3. Both users can access each other's data because both match user_id LIKE 'anon_%'

Additional Security Issues Identified

1. Mixed Authentication Systems

• Uses both Supabase anonymous auth AND client-side generated IDs
• Creates confusion and potential bypass mechanisms
• Client-side user IDs can be manipulated via localStorage

2. No Rate Limiting

• No protection against data scraping or abuse
• Anonymous users can perform unlimited database queries

Required Fixes

Immediate (Critical)

• Fix RLS policies to use exact user matching only
• Remove wildcard anon_% patterns from all policies
• Implement proper user isolation

High Priority

• Standardize on Supabase anonymous auth only
• Remove client-side user ID generation
• Remove localStorage user_id manipulation

Medium Priority

• Add rate limiting and abuse prevention
• Implement audit logging
• Add security monitoring

Proposed Solution

1. Fix RLS Policies

-- Remove dangerous wildcard, use exact match only
CREATE POLICY "Users can view own spending entries" ON public.spending_entries
    FOR SELECT USING (user_id = auth.jwt()->>'sub');

2. Standardize Authentication

• Use only Supabase's built-in anonymous authentication
• Remove all client-side user ID generation
• Remove localStorage user_id storage

Files Affected

• SUPABASE_SETUP.md - Contains vulnerable RLS policies
• src/composables/useAuth.ts - Mixed authentication logic
• All database policies need immediate review

Priority

This is a production-critical security vulnerability that must be addressed immediately before any further development or deployment.

🤖 Generated with Claude Code