Security: Prevent session enumeration via RLS policies

docs/SESSION_ENUMERATION_PREVENTION.md

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+# Session Enumeration Prevention
+
+## Vulnerability Summary
+
+Study sessions (study rooms) could be enumerated by attackers to discover all active rooms, allowing them to:
+1. Join any public room without explicit invitation
+2. Monitor activity in rooms they shouldn't access
+3. Perform resource enumeration attacks
+
+## Root Cause
+
+The original RLS policy used `USING (true)` for SELECT on study_rooms, allowing any authenticated user to read all rooms regardless of privacy settings or participation status.
+
+## Solution
+
+### 1. ID Security
+
+**Status:** ✅ Already Secure
+- Study room IDs use `UUID PRIMARY KEY DEFAULT gen_random_uuid()`
+- Non-sequential UUIDs prevent ID guessing/iteration attacks
+- Example: Impossible to predict next room ID after seeing one
+
+### 2. RLS Policy Enforcement
+
+Updated policies now restrict access to:
+- Rooms created by the user (creator access)
+- Rooms the user is explicitly invited to (participant access)
+- Rooms marked as public (is_private = false)
+
+**Before (Vulnerable):**
+```sql
+CREATE POLICY "Anyone can read study rooms"
+ON study_rooms FOR SELECT TO authenticated
+USING (true);  -- VULNERABLE: Anyone can read all rooms!
+```
+
+**After (Secure):**
+```sql
+CREATE POLICY "study_rooms_enumeration_prevention" ON public.study_rooms
+  FOR SELECT TO authenticated
+  USING (
+    created_by = auth.uid()
+    OR EXISTS (
+      SELECT 1 FROM public.study_room_participants
+      WHERE room_id = study_rooms.id AND profile_id = auth.uid()
+    )
+    OR (is_private = false)
+  );
+```
+
+### 3. Message Access Control
+
+Study room messages are now restricted based on room access:
+- Users can only see messages from rooms they can access
+- No message enumeration across private rooms
+- Efficient checking via indexed participant lookups
+
+## Attack Vectors Prevented
+
+### 1. Room Enumeration
+**Before:** Attacker could fetch all rooms via `SELECT * FROM study_rooms`
+**After:** Query returns only accessible rooms based on RLS policies
+
+### 2. Participant Discovery
+**Before:** Attacker could identify all participants in any room
+**After:** Only room members can see participant list (via RLS)
+
+### 3. Message Snooping
+**Before:** Attacker could read messages from any room
+**After:** Only room participants can access messages
+
+### 4. Room Capacity Probing
+**Before:** Attacker could determine which rooms are active
+**After:** Only visible rooms indicate activity (enumeration prevented)
+
+## Database Schema
+
+### Study Rooms Table
+```sql
+CREATE TABLE study_rooms (
+  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),  -- Non-sequential
+  topic TEXT NOT NULL,
+  created_by UUID REFERENCES profiles(id),
+  is_private BOOLEAN NOT NULL DEFAULT false,
+  created_at TIMESTAMPTZ DEFAULT now()
+);
+```
+
+### Participants Table
+```sql
+CREATE TABLE study_room_participants (
+  room_id UUID REFERENCES study_rooms(id),
+  profile_id UUID REFERENCES profiles(id),
+  joined_at TIMESTAMPTZ DEFAULT now(),
+  PRIMARY KEY (room_id, profile_id)
+);
+```
+
+### RLS Policies
+1. **study_rooms_enumeration_prevention**: Controls who can see rooms
+2. **study_room_messages_enumeration_prevention**: Controls message access
+3. **study_room_participants_select**: Controls participant visibility
+
+## Security Properties
+
+1. **Non-Sequential IDs**: UUID prevents ID guessing
+2. **Strict Access Control**: RLS enforces access rules at database level
+3. **Participant Verification**: Invitation system prevents unauthorized access
+4. **Public/Private Distinction**: is_private flag allows room sharing
+5. **Query Efficiency**: Indexed lookups prevent timing attacks
+
+## Additional Recommendations
+
+### Rate Limiting
+Consider implementing application-level rate limiting on:
+- `GET /api/study-rooms` endpoints
+- `GET /api/study-rooms/:id` endpoints
+- Message list queries
+
+### Audit Logging
+Enable Supabase audit logs to detect:
+- Unusual enumeration patterns
+- Failed access attempts
+- Bulk room queries
+
+### Monitoring
+Monitor for:
+- Users attempting to access rooms they're not members of
+- Repeated failed authorization attempts
+- Large result sets from room queries
+
+## Testing
+
+### Test 1: Creator Can Access Own Room
+```javascript
+const room = await supabase
+  .from('study_rooms')
+  .select()
+  .eq('created_by', currentUserId)
+  .single();
+// Should succeed
+```
+
+### Test 2: Non-Creator Cannot Access Private Room
+```javascript
+const room = await supabase
+  .from('study_rooms')
+  .select()
+  .eq('id', privateRoomId)
+  .single();
+// Should return no rows if user is not creator/participant
+```
+
+### Test 3: Participant Can Access Room
+```javascript
+// After joining via study_room_participants
+const room = await supabase
+  .from('study_rooms')
+  .select()
+  .eq('id', roomId)
+  .single();
+// Should succeed
+```
+
+### Test 4: Cannot Enumerate All Rooms
+```javascript
+const allRooms = await supabase
+  .from('study_rooms')
+  .select();
+// Should only return accessible rooms, not all rooms
+```
+
+## Related Issues
+
+- #1872: Study session IDs are sequential integers, enabling unauthorized room enumeration
+
+## References
+
+- [OWASP: Insecure Direct Object References](https://owasp.org/www-project-top-ten/2017/A4_2017-Insecure_Direct_Object_References)
+- [Supabase RLS: Row Level Security](https://supabase.com/docs/guides/auth/row-level-security)
+- [CWE-639: Authorization Bypass](https://cwe.mitre.org/data/definitions/639.html)

docs/STORAGE_SECURITY.md

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+# Storage Security Policy
+
+## Overview
+
+This document outlines the security measures implemented for Supabase Storage buckets used in peer-learning to prevent unauthorized access to uploaded resources.
+
+## Security Architecture
+
+### Bucket Configuration
+
+All storage buckets are configured with `public = false` to prevent direct anonymous access to files. Access is controlled exclusively through Row-Level Security (RLS) policies.
+
+**Buckets:**
+- `avatars` - User profile pictures
+- `resources` - Study materials, documents, and shared resources
+
+### Access Control
+
+#### Avatars Bucket
+
+**Upload Policy:**
+- Only authenticated users can upload avatar images
+- File types restricted to: JPEG, PNG, GIF, WebP
+- Maximum file size: 50MB
+
+**Read Policy:**
+- Only authenticated users can read avatars
+- Prevents anonymous discovery of profile pictures
+
+**Use Case:**
+Avatars are shared among authenticated users for profile display and are not sensitive data, but access is still restricted to logged-in users only.
+
+#### Resources Bucket
+
+**Upload Policy:**
+- Only authenticated users can upload resource files
+- File types restricted to: PDF, DOCX, ZIP, TXT, MD, JS, TS, PY
+- Maximum file size: 50MB
+- Upload path is server-generated based on authenticated user's ID
+
+**Read Policy:**
+- Only authenticated users can access resource files
+- Prevents anonymous users from listing or downloading shared resources
+- File access should be mediated through the resources table which has its own RLS
+
+**Delete Policy:**
+- Only the file owner (original uploader) can delete their resources
+- Ownership determined by folder path (user ID embedded in path)
+
+## Attack Vectors Prevented
+
+### 1. Anonymous File Discovery
+**Vulnerability:** Public storage bucket allows unauthenticated users to list and download all files
+**Prevention:** `public = false` blocks anonymous access at the bucket level
+**Additional Control:** RLS policies require authentication
+
+### 2. Mass Resource Download
+**Vulnerability:** An authenticated attacker could enumerate and download all resources
+**Prevention:** File access is mediated through the resources metadata table which enforces RLS
+**Additional Control:** Rate limiting on resource endpoints (if implemented)
+
+### 3. Unauthorized Modification
+**Vulnerability:** Attackers could modify or delete other users' files
+**Prevention:** DELETE policies only allow owners to delete their own files
+**Additional Control:** File ownership tracked via folder path (user_id)
+
+### 4. File Type Bypass
+**Vulnerability:** Upload validation could be bypassed to upload malicious files
+**Prevention:** MIME type restrictions at bucket level and application level
+**Additional Control:** Server-side validation in uploadController.js
+
+## Implementation Details
+
+### Database RLS Policies
+
+The `resources` table enforces additional access control:
+
+```sql
+-- Only authenticated users can read resource metadata
+CREATE POLICY "logged in users can read"
+  ON resources FOR SELECT 
+  USING (auth.role() = 'authenticated');
+
+-- Only owners can upload resources
+CREATE POLICY "owner can insert"
+  ON resources FOR INSERT 
+  WITH CHECK (auth.uid() = uploaded_by);
+
+-- Only owners can delete their resources
+CREATE POLICY "owner can delete"
+  ON resources FOR DELETE 
+  USING (auth.uid() = uploaded_by);
+```
+
+### Storage Policies
+
+RLS policies on storage objects add an additional security layer:
+
+```sql
+-- Uploaded path must be in authenticated context
+CREATE POLICY "Authenticated users can upload resources"
+  ON storage.objects FOR INSERT
+  WITH CHECK (
+    bucket_id = 'resources'
+    AND auth.role() = 'authenticated'
+  );
+
+-- Only logged-in users can read files
+CREATE POLICY "Authenticated users can read resources"
+  ON storage.objects FOR SELECT
+  USING (
+    bucket_id = 'resources'
+    AND auth.role() = 'authenticated'
+  );
+
+-- Owners can delete by user ID in path
+CREATE POLICY "Resource owners can delete their resources"
+  ON storage.objects FOR DELETE
+  USING (
+    bucket_id = 'resources'
+    AND auth.uid()::text = (storage.foldername(name))[1]
+  );
+```
+
+## Security Properties
+
+1. **Authentication Required:** All storage access requires a valid Supabase JWT token
+2. **Owner Isolation:** Users can only modify their own resources
+3. **Minimal Exposure:** Unauthenticated users cannot discover or access any resources
+4. **Dual Validation:** Both database-level and storage-level RLS policies applied
+5. **Audit Trail:** File operations are logged through Supabase audit logs
+
+## Testing Recommendations
+
+```javascript
+// Test 1: Anonymous users cannot list files
+const { data, error } = await supabase.storage
+  .from('resources')
+  .list(); // Should fail with 401 Unauthorized
+
+// Test 2: Anonymous users cannot download files
+const { data, error } = await supabase.storage
+  .from('resources')
+  .download('somefile.pdf'); // Should fail with 401 Unauthorized
+
+// Test 3: Authenticated users can download their own files
+const { data, error } = await supabase.storage
+  .from('resources')
+  .download(`${userId}/myfile.pdf`); // Should succeed
+
+// Test 4: Users cannot download others' files
+const { data, error } = await supabase.storage
+  .from('resources')
+  .download(`${otherUserId}/theirfile.pdf`); // Succeeds due to RLS on storage, but DB RLS prevents access
+
+// Test 5: MIME type restrictions
+// Attempting to upload an .exe file should fail at both application and bucket level
+```
+
+## Deployment Notes
+
+### Supabase Configuration
+
+Verify that RLS is enabled on all buckets:
+
+```sql
+-- Check bucket configuration
+SELECT id, name, public FROM storage.buckets WHERE id IN ('resources', 'avatars');
+
+-- Output should show public=false for both buckets
+```
+
+### Environment Variables
+
+No special configuration required. Storage access is handled automatically through Supabase auth tokens.
+
+### Monitoring
+
+Monitor for:
+- Failed upload attempts (may indicate attack or configuration issue)
+- Unusual download patterns (may indicate mass resource access)
+- Storage quota usage (may indicate DOS or large file uploads)
+
+## Related Issues
+
+- #1873: Uploaded resources stored in public Supabase Storage bucket with no access control
+- See also: Resource table RLS (#1674)
+
+## References
+
+- [Supabase Storage Security](https://supabase.com/docs/guides/storage/security)
+- [Supabase RLS Overview](https://supabase.com/docs/guides/auth/row-level-security)