No Privilege Escalation via Parameter Tampering

Spreading req.body directly into a db.user.update({ data: body }) call is mass assignment (CWE-915): any field the attacker includes in the request body will be written to the database. For user records, this means { "role": "admin" } is a single-request privilege escalation. CWE-285 (Improper Authorization) and OWASP A01 (Broken Access Control) cover this exact pattern. NIST 800-53 AC-6 (Least Privilege) requires that users cannot update fields beyond their entitlement — without an explicit allowlist, every field in the database schema is implicitly writable by authenticated users.

Parse update requests through a Zod schema that explicitly includes only safe profile fields. Zod silently strips any extra fields — including role, permissions, or isAdmin — before the data reaches the database.

// lib/schemas/user.ts
export const ProfileUpdateSchema = z.object({
  displayName: z.string().min(1).max(50).optional(),
  bio: z.string().max(500).optional(),
  avatarUrl: z.string().url().optional(),
  // 'role', 'permissions', 'isAdmin' are intentionally absent
});

// app/api/users/[id]/route.ts
export async function PATCH(req: NextRequest, { params }) {
  const session = await auth();
  if (!session || session.user.id !== params.id) {
    return NextResponse.json({ error: 'Forbidden' }, { status: 403 });
  }
  const data = ProfileUpdateSchema.parse(await req.json()); // Strips sensitive fields
  await db.user.update({ where: { id: params.id }, data });
}

Add .strict() to the schema to reject (rather than silently strip) requests that include unexpected fields — this surfaces integration bugs faster.

• ID: no-privilege-escalation-params

• Severity: high

• What to look for: Count all relevant instances and enumerate each. Find user update endpoints — PATCH /api/users/[id], PUT /api/profile, updateUser Server Actions. Check how request body data is applied to the database update. Specifically: is ...body or req.body spread directly into a db.user.update({ data: body }) call? Are sensitive fields like role, permissions, isAdmin, plan, credits, subscriptionStatus in the update schema? This is a mass assignment vulnerability.

• Pass criteria: User update endpoints use an explicit allowlist of updatable fields (via Zod schema or manual field selection) that excludes sensitive fields. At least 1 implementation must be verified. The request body cannot contain role, permissions, isAdmin, or similar fields that would be applied.

• Fail criteria: Any user update endpoint spreads the request body directly into a database update without filtering out sensitive fields, or a Zod schema for user updates includes role, permissions, or similar fields without requiring admin authority.

• Skip (N/A) when: No user update endpoints found in the codebase.

• Detail on fail: "User update at [route] may allow mass assignment. Sensitive fields (role, permissions, isAdmin) could be updated via the request body." (Note the specific file and the pattern used.)

• Remediation: Always use an explicit field allowlist for user updates. Zod's .pick() or .omit() methods are the easiest way to enforce this.

  // lib/schemas/user.ts
  // This schema only allows safe profile fields — no role, no permissions
  export const ProfileUpdateSchema = z.object({
    displayName: z.string().min(1).max(50).optional(),
    bio: z.string().max(500).optional(),
    avatarUrl: z.string().url().optional(),
  });
  
  // app/api/users/[id]/route.ts
  export async function PATCH(req: NextRequest, { params }) {
    const session = await auth();
    if (!session || session.user.id !== params.id) {
      return NextResponse.json({ error: 'Forbidden' }, { status: 403 });
    }
    const data = ProfileUpdateSchema.parse(await req.json()); // Strips any extra fields
    await db.user.update({ where: { id: params.id }, data });
  }
  

  The key is that ProfileUpdateSchema.parse() will strip any fields not in the schema — so even if an attacker sends { "role": "admin" }, Zod will discard it silently (or throw if .strict() is used).