v0 Security: Public Environment Variables

For a v0 app using Next.js, NEXT_PUBLIC_ is a signal that a variable can be included in browser code. Private credentials belong behind a server boundary, and that boundary must remain intact when you return data to the frontend.

This review focuses on the app you build and deploy. Platform security features help with development, but they do not determine whether your own billing, database or account-management flow makes the right authorization decision.

Separate public values from private capabilities

Start with names, not values. List every environment variable and label its purpose: public configuration, test-only setting, server credential or privileged administration credential.

v0 documents the distinction between server variables and NEXT_PUBLIC_ variables. Next.js explains that public-prefixed variables can be embedded in client bundles at build time. See v0 security guidance and the Next.js environment-variable guide.

A public analytics identifier may be appropriate in the browser. A secret that creates charges or administers a database is not. Check the provider’s key type and permissions before interpreting a scanner match.

Do not assume that a variable without the public prefix can never leak. Your code could still serialize it into a response, log it to a public endpoint or pass it through a server-rendered prop. Trace where it is used and what leaves the server.

Review Route Handlers and Server Actions

Take a hypothetical invoice-download action. It receives an invoice identifier, checks the user’s session and verifies that the user may access that invoice before returning the file. The ownership check should happen where the data is accessed.

Ask these questions during review:

• Can a visitor call the action without a valid session?

• Can a signed-in user substitute an identifier belonging to another account?

• Does the response contain more fields than the frontend needs?

• Is a privileged credential used only for the intended operation?

• Does an error return internal configuration or a stack trace?

Keeping the credential on the server answers only one of these questions. It does not make an overly permissive endpoint safe.

Check development, preview and production separately

v0’s external-API documentation distinguishes Development, Preview and Production environment settings. Confirm where each variable is available and which backend the deployment calls. The environment guidance describes those environments.

Use synthetic records and test accounts in preview. Verify that your production deployment does not accidentally call a preview backend or depend on a development-only setting. After changing a public build-time value, produce and verify a new build; an already-built bundle can retain its earlier value.

Write the environment matrix beside the integration code. Include the setting names and expected service environment, without credential values. This makes future changes easier to review.

Use a focused review prompt

Review this Next.js integration’s server/browser boundary. List environment-variable names without revealing values. Identify any private capability reaching client code, page data or responses. Check authentication and ownership in the server action. Propose a small fix and tests for an anonymous user, the owner and another signed-in user.

Review the diff and run those tests. Then inspect the published URL and relevant network responses using your own test records. A scanner result should identify observed exposure; your application tests should prove the authorization behavior you intended.

The v0 security scanner page explains VibeShield’s URL-based checks. Use the website security scanner alongside source review, not as a substitute for server-side access tests.

Common questions

Does NEXT_PUBLIC_ mean the value is secret but encrypted?

No. Treat the value as public. Use the provider’s intended browser configuration where appropriate, and keep private capabilities on the server.

Does a successful Vercel deployment prove the settings are safe?

No. Deployment success establishes that the application built and started. Verify configuration exposure and user permissions on the resulting deployment.