diff --git a/backend/src/controllers/contract.controller.ts b/backend/src/controllers/contract.controller.ts
index be91a850..79787f29 100644
--- a/backend/src/controllers/contract.controller.ts
+++ b/backend/src/controllers/contract.controller.ts
@@ -96,17 +96,20 @@ export async function getContracts(req: AuthRequest, res: Response): Promise<voi
       return;
     }
 
-    // Für Kundenportal-Benutzer: nur eigene + vertretene Kunden MIT Vollmacht
+    // Für Kundenportal-Benutzer: nur eigene + vertretene Kunden MIT Vollmacht.
+    // Fail-closed (Pentest R145): Portal-Token wird IMMER gescoped; fehlt wider
+    // Erwarten die customerId, ergibt das eine leere Menge (nicht alle).
     let customerIds: number[] | undefined;
-    if (req.user?.isCustomerPortal && req.user.customerId) {
-      // Eigene Customer-ID immer
-      customerIds = [req.user.customerId];
-      // Vertretene Kunden nur wenn Vollmacht erteilt
-      const representedIds: number[] = req.user.representedCustomerIds || [];
-      for (const repCustId of representedIds) {
-        const hasAuth = await authorizationService.hasAuthorization(repCustId, req.user.customerId);
-        if (hasAuth) {
-          customerIds.push(repCustId);
+    if (req.user?.isCustomerPortal) {
+      customerIds = req.user.customerId ? [req.user.customerId] : [];
+      if (req.user.customerId) {
+        // Vertretene Kunden nur wenn Vollmacht erteilt
+        const representedIds: number[] = req.user.representedCustomerIds || [];
+        for (const repCustId of representedIds) {
+          const hasAuth = await authorizationService.hasAuthorization(repCustId, req.user.customerId);
+          if (hasAuth) {
+            customerIds.push(repCustId);
+          }
         }
       }
     }
diff --git a/backend/src/controllers/creditNote.controller.ts b/backend/src/controllers/creditNote.controller.ts
index 39b8ac8c..447b9d02 100644
--- a/backend/src/controllers/creditNote.controller.ts
+++ b/backend/src/controllers/creditNote.controller.ts
@@ -66,8 +66,8 @@ export async function listAll(req: AuthRequest, res: Response): Promise<void> {
       }
     }
 
-    const page = parseInt((req.query.page as string) || '1') || 1;
-    const limit = Math.min(parseInt((req.query.limit as string) || '50') || 50, 200);
+    const page = Math.max(parseInt((req.query.page as string) || '1') || 1, 1);
+    const limit = Math.min(Math.max(parseInt((req.query.limit as string) || '50') || 50, 1), 200);
     const search = typeof req.query.search === 'string' ? req.query.search : undefined;
 
     const result = await creditNoteService.getAllCreditNotes({ customerIds, page, limit, search });
diff --git a/backend/src/services/contract.service.ts b/backend/src/services/contract.service.ts
index f2758f07..7ccd831b 100644
--- a/backend/src/services/contract.service.ts
+++ b/backend/src/services/contract.service.ts
@@ -21,8 +21,11 @@ export async function getAllContracts(filters: ContractFilters) {
 
   const where: Record<string, unknown> = {};
 
-  // Entweder einzelne customerId ODER Liste von customerIds (für Kundenportal)
-  if (customerIds && customerIds.length > 0) {
+  // Entweder Liste von customerIds (Kundenportal, fail-closed) ODER einzelne
+  // customerId (Staff-Filter). Fail-closed (Pentest R145): ist customerIds
+  // gesetzt – auch als LEERES Array – wird strikt darauf gefiltert (`IN ()`
+  // → 0 Treffer). Nur `undefined` (Staff) überspringt den Filter.
+  if (customerIds) {
     where.customerId = { in: customerIds };
   } else if (customerId) {
     where.customerId = customerId;