Vite is a website frontend framework. When Vite's HTML transformation is invoked manually via server.transformIndexHtml, the original request URL is passed in unmodified, and the html being transformed contains inline module scripts (<script type="module">...</script>), it is possible to inject arbitrary HTML into the transformed output by supplying a malicious URL query string to server.transformIndexHtml. Only apps using appType: 'custom' and using the default Vite HTML middleware are affected.

The HTML entry must also contain an inline script. The attack requires a user to click on a malicious URL while running the dev server. Restricted files aren't exposed to the attacker.

This issue has been addressed in vite@5.0.5, vite@4.5.1, and vite@4.4.12. There are no known workarounds for this vulnerability.