fix(backend): IDOR in POST /notifications/:id/read (Modul 26)

markRead() pruefte bisher nicht, ob die Benachrichtigung dem
anfragenden Nutzer gehoert - jeder authentifizierte Nutzer konnte
fremde Benachrichtigungen als gelesen markieren. Jetzt: 403 bei
fremder Benachrichtigung, weiterhin erlaubt fuer eigene und
Broadcast-Benachrichtigungen (userId = null). E2E-Regressionstest
ergaenzt.

ApiCore-Backend/src/notifications/notifications.controller.ts

@@ -22,7 +22,7 @@ export class NotificationsController {
   }
 
   @Post(':id/read')
-  markRead(@Param('id') id: string) {
-    return this.notificationsService.markRead(id);
+  markRead(@Param('id') id: string, @CurrentUser() actor: AuthenticatedUser) {
+    return this.notificationsService.markRead(id, actor.id);
   }
 }

ApiCore-Backend/src/notifications/notifications.service.spec.ts

@@ -1,4 +1,4 @@
-import { NotFoundException } from '@nestjs/common';
+import { ForbiddenException, NotFoundException } from '@nestjs/common';
 import { NotificationsService } from './notifications.service';
 import { PrismaService } from '../prisma/prisma.service';
 
@@ -55,19 +55,44 @@ describe('NotificationsService', () => {
 
   it('throws NotFoundException when marking an unknown notification as read', async () => {
     prisma.notification.findUnique.mockResolvedValueOnce(null);
-    await expect(service.markRead('missing')).rejects.toBeInstanceOf(
+    await expect(service.markRead('missing', 'user-1')).rejects.toBeInstanceOf(
       NotFoundException,
     );
   });
 
-  it('marks a notification as read', async () => {
+  it("throws ForbiddenException when marking another user's notification as read", async () => {
     prisma.notification.findUnique.mockResolvedValueOnce({
       id: 'n1',
+      userId: 'owner',
+      read: false,
+    });
+    await expect(service.markRead('n1', 'someone-else')).rejects.toBeInstanceOf(
+      ForbiddenException,
+    );
+  });
+
+  it('marks a broadcast notification (no owner) as read for any user', async () => {
+    prisma.notification.findUnique.mockResolvedValueOnce({
+      id: 'n1',
+      userId: null,
       read: false,
     });
     prisma.notification.update.mockResolvedValueOnce({ id: 'n1', read: true });
 
-    const result = await service.markRead('n1');
+    const result = await service.markRead('n1', 'any-user');
+
+    expect(result.read).toBe(true);
+  });
+
+  it("marks the owner's own notification as read", async () => {
+    prisma.notification.findUnique.mockResolvedValueOnce({
+      id: 'n1',
+      userId: 'user-1',
+      read: false,
+    });
+    prisma.notification.update.mockResolvedValueOnce({ id: 'n1', read: true });
+
+    const result = await service.markRead('n1', 'user-1');
 
     expect(result.read).toBe(true);
   });

ApiCore-Backend/src/notifications/notifications.service.ts

@@ -1,4 +1,8 @@
-import { Injectable, NotFoundException } from '@nestjs/common';
+import {
+  ForbiddenException,
+  Injectable,
+  NotFoundException,
+} from '@nestjs/common';
 import { PrismaService } from '../prisma/prisma.service';
 import { Notification, NotificationPriority } from '../../generated/prisma';
 
@@ -36,13 +40,16 @@ export class NotificationsService {
     });
   }
 
-  async markRead(id: string): Promise<Notification> {
+  async markRead(id: string, actingUserId: string): Promise<Notification> {
     const notification = await this.prisma.notification.findUnique({
       where: { id },
     });
     if (!notification) {
       throw new NotFoundException('Notification not found');
     }
+    if (notification.userId !== null && notification.userId !== actingUserId) {
+      throw new ForbiddenException("Cannot modify another user's notification");
+    }
     return this.prisma.notification.update({
       where: { id },
       data: { read: true },