Apply Next.js App Router data-security best practices for RSC, Data Access Layers, DTOs, server-only modules, React taint, and Server Actions (authn/authz, input validation, return minimization, CSRF origins). Use when reviewing or implementing data fetching, mutations, secret handling, IDOR prevention, client prop exposure, or "use server"/"use client" security; when the user runs /vercel-data-security-guide or mentions Next.js data security, RSC data leaks, or Server Action security.
