My confidential environment variables are being inadvertently revealed to the client by Next.js

Question

My confidential environment variables are being inadvertently revealed to the client by Next.js

I am encountering a problem with my project in which an environment variable is being revealed to the browser. Despite the documentation stating that only environment variables prefixed with NEXT_PUBLIC_ should be accessible in the browser environment, all of my environment variables are being exposed.

Here's an example: .env.local:

SECRET=SECRET_VALUE

/app/page.tsx

export default function Home(){
  return (
    <div>{process.env.SECRET}</div>
  )
}

The code above displays the value "SECRET_VALUE" in the browser. Here is a straightforward code snippet to reproduce the issue.

Thank you in advance.

javascript next.js

Answer 1

Answer №1

Your page is displaying `process.env.secret` because it is being rendered on the server by default, where environment variables are accessible. When the server renders your page, it reads the env variable value and displays it in the DOM.

To prevent exposing your env variable to the client, you can add `use client` at the top of `/app/page.tsx` to mark it as part of the client bundle rendered by React on the client side. This may cause a hydration error, which is discussed in more detail here.

For a fully functional demo without the hydration error, use the code below and compare the `console.log` values in your terminal with those in the browser:


'use client';

export default function Home() {
  console.log('env variable is: ', process.env.SECRET);

  return <div>Compare console log values in app terminal and browser</div>;
}

Answer 2

Your page is displaying `process.env.secret` because it is being rendered on the server by default, where environment variables are accessible. When the server renders your page, it reads the env variable value and displays it in the DOM.

To prevent exposing your env variable to the client, you can add `use client` at the top of `/app/page.tsx` to mark it as part of the client bundle rendered by React on the client side. This may cause a hydration error, which is discussed in more detail here.

For a fully functional demo without the hydration error, use the code below and compare the `console.log` values in your terminal with those in the browser:


'use client';

export default function Home() {
  console.log('env variable is: ', process.env.SECRET);

  return <div>Compare console log values in app terminal and browser</div>;
}

My confidential environment variables are being inadvertently revealed to the client by Next.js

Answer №1

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