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colaflow-api/SECURITY-FIX-CROSS-TENANT-ACCESS.md

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+# SECURITY FIX: Cross-Tenant Access Validation
+
+## Executive Summary
+
+**Status**: IMPLEMENTED ✓
+**Priority**: CRITICAL
+**Date**: 2025-11-03
+**Modified Files**: 1
+**Build Status**: SUCCESS (0 warnings, 0 errors)
+
+## Security Vulnerability
+
+### Issue Identified
+During Day 6 integration testing, a critical security gap was discovered in the Role Management API (`TenantUsersController`):
+
+**Vulnerability**: Users from Tenant A could access and potentially manage Tenant B's users and roles by manipulating the `tenantId` route parameter.
+
+**Impact**:
+- Unauthorized access to other tenants' user lists
+- Potential unauthorized role assignments across tenants
+- Breach of multi-tenant data isolation principles
+
+**Severity**: HIGH - Violates fundamental security principle of tenant isolation
+
+## Implementation
+
+### Modified File
+`src/ColaFlow.API/Controllers/TenantUsersController.cs`
+
+### Endpoints Fixed
+
+| Endpoint | Method | Authorization Policy | Validation Added |
+|----------|--------|---------------------|------------------|
+| `/api/tenants/{tenantId}/users` | GET | RequireTenantAdmin | ✓ Yes |
+| `/api/tenants/{tenantId}/users/{userId}/role` | POST | RequireTenantOwner | ✓ Yes |
+| `/api/tenants/{tenantId}/users/{userId}` | DELETE | RequireTenantOwner | ✓ Yes |
+| `/api/tenants/../roles` | GET | RequireTenantAdmin | N/A (Static data) |
+
+### Validation Logic
+
+Each protected endpoint now includes:
+
+```csharp
+// SECURITY: Validate user belongs to target tenant
+var userTenantIdClaim = User.FindFirst("tenant_id")?.Value;
+if (userTenantIdClaim == null)
+    return Unauthorized(new { error = "Tenant information not found in token" });
+
+var userTenantId = Guid.Parse(userTenantIdClaim);
+if (userTenantId != tenantId)
+    return StatusCode(403, new { error = "Access denied: You can only manage users in your own tenant" });
+```
+
+### Security Flow
+
+1. **Extract JWT Claim**: Read `tenant_id` from authenticated user's JWT token
+2. **Claim Validation**: Return 401 Unauthorized if `tenant_id` claim is missing
+3. **Tenant Matching**: Compare user's tenant ID with route parameter `tenantId`
+4. **Access Control**: Return 403 Forbidden if tenant IDs don't match
+5. **Proceed**: Continue to business logic only if validation passes
+
+## Expected Behavior After Fix
+
+### Scenario 1: Same Tenant Access (Authorized)
+```
+User: Tenant A Admin (tenant_id = "aaaa-1111")
+Request: GET /api/tenants/aaaa-1111/users
+Result: 200 OK + User list
+```
+
+### Scenario 2: Cross-Tenant Access (Blocked)
+```
+User: Tenant A Admin (tenant_id = "aaaa-1111")
+Request: GET /api/tenants/bbbb-2222/users
+Result: 403 Forbidden + Error message
+```
+
+### Scenario 3: Missing Tenant Claim (Invalid Token)
+```
+User: Token without tenant_id claim
+Request: GET /api/tenants/aaaa-1111/users
+Result: 401 Unauthorized + Error message
+```
+
+## Verification
+
+### Build Status
+```
+Build succeeded.
+    0 Warning(s)
+    0 Error(s)
+
+Time Elapsed 00:00:02.24
+```
+
+### Code Quality
+- ✓ Consistent validation pattern across all endpoints
+- ✓ Clear security comments explaining purpose
+- ✓ Proper HTTP status codes (401 vs 403)
+- ✓ Descriptive error messages
+- ✓ No code duplication (same pattern repeated)
+
+## Technical Details
+
+### JWT Claim Structure
+The `tenant_id` claim is added by `JwtService.GenerateToken()`:
+```csharp
+new("tenant_id", tenant.Id.ToString())
+```
+
+Location: `src/Modules/Identity/ColaFlow.Modules.Identity.Infrastructure/Services/JwtService.cs` (Line 34)
+
+### Authorization Policies (Unchanged)
+Existing policies remain in place:
+- `RequireTenantOwner` - Checks for TenantOwner role
+- `RequireTenantAdmin` - Checks for TenantAdmin or TenantOwner role
+
+**Important**: These policies validate **roles**, while the new validation checks **tenant membership**.
+
+### Why GetAvailableRoles Doesn't Need Validation
+The `/api/tenants/../roles` endpoint returns static role definitions (TenantOwner, TenantAdmin, etc.) and doesn't access tenant-specific data. The existing `RequireTenantAdmin` policy is sufficient.
+
+## Security Best Practices Followed
+
+1. **Defense in Depth**: Validation at API layer before business logic
+2. **Fail Securely**: Return 403 Forbidden on mismatch (don't reveal if tenant exists)
+3. **Clear Error Messages**: Help legitimate users understand authorization failures
+4. **Consistent Implementation**: Same pattern across all endpoints
+5. **Minimal Changes**: API-layer validation only, no changes to command handlers or repositories
+
+## Remaining Work
+
+### Testing Recommendations
+1. **Unit Tests**: Add tests for tenant validation logic
+2. **Integration Tests**: Update `RoleManagementTests.cs` to verify cross-tenant blocking
+3. **Security Testing**: Penetration test with cross-tenant attack scenarios
+
+### Future Enhancements
+1. **Centralized Validation**: Consider extracting to an action filter or middleware
+2. **Audit Logging**: Log all 403 responses for security monitoring
+3. **Rate Limiting**: Add rate limiting on 403 responses to prevent tenant enumeration
+
+## References
+
+- **Original Report**: `DAY6-TEST-REPORT.md` - Section "Cross-Tenant Access Validation"
+- **JWT Service**: `src/Modules/Identity/ColaFlow.Modules.Identity.Infrastructure/Services/JwtService.cs`
+- **Modified Controller**: `src/ColaFlow.API/Controllers/TenantUsersController.cs`
+- **Authorization Policies**: `src/ColaFlow.API/Program.cs` (Lines configuring authorization)
+
+## Sign-Off
+
+**Implemented By**: Backend Agent (Claude Code)
+**Reviewed By**: Pending code review
+**Status**: Ready for integration testing
+**Next Steps**:
+1. User to commit the staged changes (1Password SSH signing required)
+2. Add integration tests to verify cross-tenant blocking
+3. Deploy to staging environment for security testing
+
+---
+
+**Note**: The implementation is complete and builds successfully. The file is staged for commit but cannot be committed automatically due to 1Password SSH signing configuration requiring user interaction.