Kimai's API invoice endpoint missing customer-level access control (IDOR)

Summary

GET /api/invoices/{id} only checks the role-based view_invoice permission but does not verify the requesting user has access to the invoice's customer. Any user with ROLE_TEAMLEAD (which grants view_invoice) can read all invoices in the system, including those belonging to customers assigned to other teams.

Affected Code

src/API/InvoiceController.php line 92-101:

#[IsGranted('view_invoice')]           // Role check only, no customer access check
#[Route(methods: ['GET'], path: '/{id}', name: 'get_invoice', requirements: ['id' => '\d+'])]
public function getAction(Invoice $invoice): Response
{
    $view = new View($invoice, 200);
    $view->getContext()->setGroups(self::GROUPS_ENTITY);
    return $this->viewHandler->handle($view);  // Returns ANY invoice by ID
}

The web controller (src/Controller/InvoiceController.php line 304-307) correctly checks customer access:

#[IsGranted('view_invoice')]
#[IsGranted(new Expression("is_granted('access', subject.getCustomer())"), 'invoice')]
public function downloadAction(Invoice $invoice, ...): Response { ... }

The access attribute in CustomerVoter (line 71-87) verifies team membership, but this check is entirely missing from the API endpoint.

PoC

Tested against Kimai v2.50.0 (Docker: kimai/kimai2:apache).

Setup:

• TeamA with CustomerA ("SecretCorp"), TeamB with CustomerB ("BobCorp")
• Bob is a teamlead in TeamB only
• An invoice exists for SecretCorp (TeamA)

# Bob (TeamB) reads SecretCorp (TeamA) invoice
curl -H "Authorization: Bearer BOB_TOKEN" http://localhost:8888/api/invoices/1

Response (200 OK):

{
  "invoiceNumber": "INV-2026-001",
  "total": 15000.0,
  "currency": "USD",
  "customer": {"name": "SecretCorp", ...}
}

Bob can also enumerate all invoices via GET /api/invoices — the list endpoint uses setCurrentUser() in the query but the single-item endpoint bypasses this entirely via Symfony ParamConverter.

Impact

Any teamlead can read all invoices across the system regardless of team assignment. Invoice data typically contains sensitive financial information (amounts, customer details, payment terms). In multi-team deployments this breaks the intended data isolation between teams.

Suggested Fix

Add the customer access check to the API endpoint, matching the web controller:

 #[IsGranted('view_invoice')]
+#[IsGranted(new Expression("is_granted('access', subject.getCustomer())"), 'invoice')]
 #[Route(methods: ['GET'], path: '/{id}', name: 'get_invoice')]
 public function getAction(Invoice $invoice): Response