Fix Mass Assignment in Qwik

Mass Assignment in Qwik occurs when untrusted user input is directly merged into sensitive data models or database queries. In Qwik City, this typically happens within 'routeAction$' handlers where 'formData' or action arguments are spread into a persistence layer without filtering, allowing attackers to overwrite protected fields like 'role', 'permissions', or 'is_admin'.

The Vulnerable Pattern

export const useUpdateProfile = routeAction$(async (data) => {
  // VULNERABLE: Spreading the entire 'data' object directly into the database update
  // An attacker can append 'isAdmin: true' to the POST body to escalate privileges
  await db.user.update({
    where: { id: data.userId },
    data: { ...data }
  });
});

The Secure Implementation

The fix involves two layers of defense: Schema Validation and Allowlisting. By using 'zod$' inside the 'routeAction$', we enforce a strict contract that strips any undeclared fields from the input. Furthermore, instead of using the spread operator (...data), we explicitly destructure only the fields ('bio', 'avatarUrl') that are safe for the user to modify. This ensures that even if a malicious payload contains 'role: "admin"', it is ignored by the application logic.

import { z, zod$ } from '@builder.io/qwik-city';
// SECURE: Define a strict schema to filter input and use explicit mapping
export const useUpdateProfile = routeAction$(
async (data) => {
const { bio, avatarUrl } = data;
await db.user.update({
where: { id: data.userId },
data: { bio, avatarUrl }
});
},
zod$({
bio: z.string().max(160),
avatarUrl: z.string().url()
})
);