diff --git a/LEARNINGS.md b/LEARNINGS.md
index 4b78948..f075852 100644
--- a/LEARNINGS.md
+++ b/LEARNINGS.md
@@ -534,5 +534,14 @@ Der Admin-Settings-Endpunkt (`GET /api/admin/settings`) erfordert `global_admin`
 ### 2026-07-22 | Workflow-Editor | _legacy_dispatch umging cancelled/rejected Pre-Check
 `_legacy_dispatch` in `dispatch_service.py` rief `render_order_line_task.delay()` direkt auf und umging damit den Pre-Check in `dispatch_order_line_render` (der cancelled/rejected Lines überspringt). Alle Legacy-Dispatch-Pfade (auch im Graph-Fallback) liefen so durch, auch für bereits gecancelte Jobs. **Lösung:** `_legacy_dispatch` ruft jetzt `dispatch_order_line_render.delay()` auf statt `render_order_line_task.delay()` direkt.
 
+### 2026-07-22 | Security | Billing-Rechnungen ohne Tenant-Isolation
+`list_invoices` in `billing/router.py` übergab `tenant_id` nicht an `get_invoices`. `get_invoices` im Service ignorierte den Parameter — kein WHERE-Filter vorhanden. Jeder `admin_or_pm`-User konnte alle Rechnungen aller Tenants sehen. **Lösung:** Router extrahiert `tenant_id` aus `current_user` (nur wenn nicht `global_admin`), Service filtert mit `.where(Invoice.tenant_id == tenant_id)`. `get_invoice_endpoint` prüft zusätzlich `inv.tenant_id == current_user.tenant_id` für Nicht-Admins.
+
+### 2026-07-22 | Security | Invoice-Status nicht validiert — beliebige Strings schreibbar
+`InvoiceStatusUpdate.status` war `str` ohne Einschränkung. `VALID_STATUSES` in `billing/service.py` war definiert aber nie referenziert. **Lösung:** `InvoiceStatusUpdate.status` auf `Literal["draft","sent","paid","cancelled"]` geändert (Pydantic-Validierung auf Schemaebene). Zusätzlich guard in `update_invoice_status` als defence-in-depth.
+
+### 2026-07-22 | Security | SMTP-Passwort im Klartext in GET /api/admin/settings
+`SettingsOut.smtp_password` gab den gespeicherten Wert an jeden `global_admin` zurück. **Lösung:** `_settings_to_out` maskiert den Wert — `"***"` wenn gesetzt, `""` wenn leer. `update_settings` überspringt das Schreiben wenn `body.smtp_password == "***"` (Sentinel für "unverändert lassen").
+
 ### 2026-07-22 | Refactoring | Turntable-Branch aus render_order_line_task extrahiert
 `render_order_line_task` war ein 427-Zeilen-Monolith. Der Turntable-Branch (~55 Zeilen) wurde in `_render_turntable(*, render_invocation, step_path, output_path, template, order_line_id, emit, pl)` ausgelagert — resolved objects als Parameter (Option B), damit Session und PipelineLogger im Main Task verbleiben und kein doppeltes DB-Lookup entsteht. Der 68-Zeilen Exception-Handler (Mark-as-failed bei max_retries) wurde in `_handle_render_task_exhausted(order_line_id, exc, tenant_id)` extrahiert; die Retry-Logik (`self.retry`) bleibt im Main Task, da sie den Celery `self`-Context benötigt. Beide Helper stehen in `render_order_line.py` vor den Task-Definitionen.
diff --git a/backend/app/api/routers/admin.py b/backend/app/api/routers/admin.py
index 6dfd7c0..21b2a77 100644
--- a/backend/app/api/routers/admin.py
+++ b/backend/app/api/routers/admin.py
@@ -232,7 +232,7 @@ def _settings_to_out(raw: dict[str, str]) -> SettingsOut:
         smtp_host=raw.get("smtp_host", ""),
         smtp_port=int(raw.get("smtp_port", "587")),
         smtp_user=raw.get("smtp_user", ""),
-        smtp_password=raw.get("smtp_password", ""),
+        smtp_password="***" if raw.get("smtp_password", "") else "",
         smtp_from_address=raw.get("smtp_from_address", ""),
         scene_linear_deflection=float(raw.get("scene_linear_deflection", "0.1")),
         scene_angular_deflection=float(raw.get("scene_angular_deflection", "0.1")),
@@ -357,7 +357,7 @@ async def update_settings(
         updates["smtp_port"] = str(body.smtp_port)
     if body.smtp_user is not None:
         updates["smtp_user"] = body.smtp_user
-    if body.smtp_password is not None:
+    if body.smtp_password is not None and body.smtp_password != "***":
         updates["smtp_password"] = body.smtp_password
     if body.smtp_from_address is not None:
         updates["smtp_from_address"] = body.smtp_from_address
diff --git a/backend/app/domains/billing/router.py b/backend/app/domains/billing/router.py
index c28463d..cbe985f 100644
--- a/backend/app/domains/billing/router.py
+++ b/backend/app/domains/billing/router.py
@@ -6,7 +6,8 @@ from fastapi.responses import Response
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.database import get_db
-from app.utils.auth import require_admin_or_pm
+from app.utils.auth import require_admin_or_pm, _role_value
+from app.domains.auth.models import ADMIN_ROLES
 from app.domains.billing.schemas import InvoiceCreate, InvoiceOut, InvoiceStatusUpdate
 from app.domains.billing.service import (
     create_invoice, get_invoices, get_invoice,
@@ -26,7 +27,8 @@ async def list_invoices(
     db: AsyncSession = Depends(get_db),
     current_user=Depends(require_admin_or_pm),
 ):
-    return await get_invoices(db, skip=skip, limit=limit)
+    tenant_id = None if _role_value(current_user) in ADMIN_ROLES else getattr(current_user, "tenant_id", None)
+    return await get_invoices(db, tenant_id=tenant_id, skip=skip, limit=limit)
 
 
 @invoice_router.post("/invoices", response_model=InvoiceOut, status_code=status.HTTP_201_CREATED)
@@ -57,6 +59,10 @@ async def get_invoice_endpoint(
     inv = await get_invoice(db, invoice_id)
     if not inv:
         raise HTTPException(status_code=404, detail="Invoice not found")
+    if _role_value(current_user) not in ADMIN_ROLES:
+        user_tenant = getattr(current_user, "tenant_id", None)
+        if inv.tenant_id != user_tenant:
+            raise HTTPException(status_code=404, detail="Invoice not found")
     return inv
 
 
diff --git a/backend/app/domains/billing/schemas.py b/backend/app/domains/billing/schemas.py
index 142bbda..85e934f 100644
--- a/backend/app/domains/billing/schemas.py
+++ b/backend/app/domains/billing/schemas.py
@@ -3,6 +3,7 @@ from __future__ import annotations
 import uuid
 from datetime import date, datetime
 from decimal import Decimal
+from typing import Literal
 from pydantic import BaseModel, computed_field
 
 
@@ -35,7 +36,7 @@ class InvoiceCreate(BaseModel):
 
 
 class InvoiceStatusUpdate(BaseModel):
-    status: str  # draft|sent|paid|cancelled
+    status: Literal["draft", "sent", "paid", "cancelled"]
 
 
 class InvoiceOut(BaseModel):
diff --git a/backend/app/domains/billing/service.py b/backend/app/domains/billing/service.py
index 3d4ca30..42b92e7 100644
--- a/backend/app/domains/billing/service.py
+++ b/backend/app/domains/billing/service.py
@@ -283,6 +283,8 @@ async def get_invoices(
         .offset(skip)
         .limit(limit)
     )
+    if tenant_id is not None:
+        q = q.where(Invoice.tenant_id == tenant_id)
     result = await db.execute(q)
     return list(result.scalars().all())
 
@@ -297,6 +299,8 @@ async def get_invoice(db: AsyncSession, invoice_id: uuid.UUID) -> Invoice | None
 
 
 async def update_invoice_status(db: AsyncSession, invoice_id: uuid.UUID, status: str) -> Invoice | None:
+    if status not in VALID_STATUSES:
+        raise ValueError(f"Invalid status '{status}'. Must be one of: {', '.join(sorted(VALID_STATUSES))}")
     invoice = await get_invoice(db, invoice_id)
     if not invoice:
         return None