Static Site Generation (SSG) creates a false sense of security. If you're hiding sensitive data behind a useEffect redirect in Gatsby, you've already lost. Attackers don't need to execute your JavaScript to bypass your 'security'; they just need to read the raw HTML response or inspect the build artifacts. Logic flow bypasses in Gatsby occur when developers treat client-side routing as a security boundary rather than a UI convenience.

The Vulnerable Pattern

import React, { useEffect } from "react"
import { navigate } from "gatsby"
const AdminDashboard = () => {
useEffect(() => {
// VULNERABLE: Logic flow bypass via client-side check
const user = JSON.parse(localStorage.getItem(“user”))
if (!user || user.role !== “admin”) {
navigate(“/login”)
}
}, [])
return (

Admin Secret: The server root password is 'P4ssw0rd!'

  )
}
export default AdminDashboard

The Secure Implementation

The vulnerable code leaks sensitive information because Gatsby pre-renders the HTML during build time or serves it before the useEffect hook executes. An attacker can use 'curl' or disable JS to view the 'Admin Secret' immediately. The secure implementation uses Gatsby's 'getServerData' (SSR). This ensures that the authorization logic happens on the server. If the user is unauthorized, the server sends a 302 redirect and never transmits the sensitive payload to the client's browser, effectively closing the bypass vector.

import React from "react"
export default function AdminDashboard({ serverData }) {
return (

Admin Secret: {serverData.secret}

  )
}
// SECURE: Server-side authorization check
export async function getServerData(context) {
const { headers } = context;
const authRes = await fetch(“https://api.yoursite.com/auth/verify”, {
headers: { cookie: headers.get(“cookie”) }
});
if (authRes.status !== 200) {
return {
status: 302,
headers: { Location: “/login” }
}
}
const data = await authRes.json();
return {
props: { secret: data.secret }
}
}