# 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

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**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.