Vitest: Servers misapply `server.fs.deny`, serving `.env`, private keys, `.git`, and the API token file

• Project servers set deny: ['.vitest-secret-token'] from a config() hook, which replaces Vite's defaults. A project server listens on a port in Browser Mode with test.projects, so in that setup a request like GET /.env?raw returns the file. A plain GET /.env is also served as text/javascript, so a malicious page can include it with <script src="http://localhost:<port>/.env">. A classic script include needs no CORS, and each dotenv line whose value is valid JavaScript (a quoted string, number, or boolean) runs as a global assignment the page can read. A syntax error anywhere in the file, such as a # comment, keeps the whole script from running. The same missing defaults also loosen Browser Mode's file-access checks for server.readFile/writeFile/removeFile, screenshots, and traces.
• The root server adds the token entry after Vite has compiled the matcher, so the entry is never applied. The token file normally lives in the per-user data directory, which is outside server.fs.allow. When that directory can't be written, for example in a container whose user has no writable HOME, Vitest falls back to <workspaceRoot>/node_modules/.vitest/.vitest-secret-token, which the root server then serves. The token authenticates the UI, /__vitest_attachment__, and the API WebSocket, whose RPC can write and rerun test files when api.allowWrite/api.allowExec are enabled.

Impact

Information disclosure from the Vitest dev server, and with the token, privileged API access.

• From a malicious website, in Browser Mode with test.projects: while the browser server runs, any page the developer visits can read .env values that are valid JavaScript, through a classic <script> include. This works when the file consists of KEY="value" lines. An unquoted value causes a runtime error that stops the script at that line, so only the lines before it leak. A syntax error anywhere in the file, such as a # comment line or an export prefix, prevents the script from running at all. Recent Chrome versions may ask for Local Network Access permission first. fetch and XHR reads from other websites are still blocked by Vite's default CORS policy, and Vite's Host check blocks DNS rebinding. That CORS policy does allow localhost origins, so a page served from another local dev server could read full files. The token file can't be read through a classic <script>, because a bare token isn't valid JavaScript.
• With local access or developer-set network exposure (such as api.host or browser.api.host, port forwarding, or a published container port): full file contents are readable over plain HTTP, including the token file when it's in the fallback location.

Only the machine running Vitest is exposed, while it runs one of the setups above. Applications built or deployed from the project aren't affected.

The fix is in vitest <PATCHED>. Vitest 4 and earlier are unaffected. They don't persist an API token, and they don't override server.fs.deny.

Workaround

Set server.fs.deny explicitly in the root Vitest config, including Vite's default list for your Vite version and the token file. For Vite 8.3:

export default defineConfig({
  server: {
    fs: {
      deny: [
        '.env',
        '.env.*',
        '*.{crt,pem,key,p12,pfx,cer,der}',
        '.npmrc',
        '.yarnrc.yml',
        '**/.git/**',
        '.vitest-secret-token',
      ],
    },
  },
})