Summary
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.
Impact
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.
Patches
Fixed in [email protected], [email protected], [email protected]
Details
Suppose index.html contains an inline module script:
<script type="module">
// Inline script
</script>
This script is transformed into a proxy script like
<script type="module" src="/index.html?html-proxy&index=0.js"></script>
due to Vite's HTML plugin:
https://github.com/vitejs/vite/blob/7fd7c6cebfcad34ae7021ebee28f97b1f28ef3f3/packages/vite/src/node/plugins/html.ts#L429-L465
When appType: 'spa' | 'mpa', Vite serves HTML itself, and htmlFallbackMiddleware rewrites req.url to the canonical path of index.html,
https://github.com/vitejs/vite/blob/73ef074b80fa7252e0c46a37a2c94ba8cba46504/packages/vite/src/node/server/middlewares/htmlFallback.ts#L44-L47
so the url passed to server.transformIndexHtml is /index.html.
However, if appType: 'custom', HTML is served manually, and if server.transformIndexHtml is called with the unmodified request URL (as the SSR docs suggest), then the path of the transformed html-proxy script varies with the request URL. For example, a request with path / produces
<script type="module" src="/@id/__x00__/index.html?html-proxy&index=0.js"></script>
It is possible to abuse this behavior by crafting a request URL to contain a malicious payload like
"></script><script>alert('boom')</script>
so a request to http://localhost:5173/?%22%3E%3C/script%3E%3Cscript%3Ealert(%27boom%27)%3C/script%3E produces HTML output like
<script type="module" src="/@id/__x00__/?"></script><script>alert("boom")</script>?html-proxy&index=0.js"></script>which demonstrates XSS.
PoC
- Example 1. Serving HTML from
vite dev middleware with appType: 'custom'
- Example 2. Serving HTML from SSR-style Express server (Vite dev server runs in middleware mode):
- Example 3. Plain
vite dev (this shows that vanilla vite dev is not vulnerable, provided htmlFallbackMiddleware is used)
Detailed Impact
This will probably predominantly affect development-mode SSR, where vite.transformHtml is called using the original req.url, per the docs:
https://github.com/vitejs/vite/blob/7fd7c6cebfcad34ae7021ebee28f97b1f28ef3f3/docs/guide/ssr.md?plain=1#L114-L126
However, since this vulnerability affects server.transformIndexHtml, the scope of impact may be higher to also include other ad-hoc calls to server.transformIndexHtml from outside of Vite's own codebase.
My best guess at bisecting which versions are vulnerable involves the following test script
import fs from 'node:fs/promises';
import * as vite from 'vite';
const html = `
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
</head>
<body>
<script type="module">
// Inline script
</script>
</body>
</html>
`;
const server = await vite.createServer({ appType: 'custom' });
const transformed = await server.transformIndexHtml('/?%22%3E%3C/script%3E%3Cscript%3Ealert(%27boom%27)%3C/script%3E', html);
console.log(transformed);
await server.close();and using it I was able to narrow down to #13581. If this is correct, then vulnerable Vite versions are 4.4.0-beta.2 and higher (which includes 4.4.0).
References
mxxk Reporter
Summary
When Vite's HTML transformation is invoked manually via
server.transformIndexHtml, the original request URL is passed in unmodified, and thehtmlbeing 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 toserver.transformIndexHtml.Impact
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.Patches
Fixed in [email protected], [email protected], [email protected]
Details
Suppose
index.htmlcontains an inline module script:This script is transformed into a proxy script like
due to Vite's HTML plugin:
https://github.com/vitejs/vite/blob/7fd7c6cebfcad34ae7021ebee28f97b1f28ef3f3/packages/vite/src/node/plugins/html.ts#L429-L465
When
appType: 'spa' | 'mpa', Vite serves HTML itself, andhtmlFallbackMiddlewarerewritesreq.urlto the canonical path ofindex.html,https://github.com/vitejs/vite/blob/73ef074b80fa7252e0c46a37a2c94ba8cba46504/packages/vite/src/node/server/middlewares/htmlFallback.ts#L44-L47
so the
urlpassed toserver.transformIndexHtmlis/index.html.However, if
appType: 'custom', HTML is served manually, and ifserver.transformIndexHtmlis called with the unmodified request URL (as the SSR docs suggest), then the path of the transformedhtml-proxyscript varies with the request URL. For example, a request with path/producesIt is possible to abuse this behavior by crafting a request URL to contain a malicious payload like
so a request to http://localhost:5173/?%22%3E%3C/script%3E%3Cscript%3Ealert(%27boom%27)%3C/script%3E produces HTML output like
which demonstrates XSS.
PoC
vite devmiddleware withappType: 'custom'?%22%3E%3C/script%3E%3Cscript%3Ealert(%27boom%27)%3C/script%3Eand navigatevite dev(this shows that vanillavite devis not vulnerable, providedhtmlFallbackMiddlewareis used)Detailed Impact
This will probably predominantly affect development-mode SSR, where
vite.transformHtmlis called using the originalreq.url, per the docs:https://github.com/vitejs/vite/blob/7fd7c6cebfcad34ae7021ebee28f97b1f28ef3f3/docs/guide/ssr.md?plain=1#L114-L126
However, since this vulnerability affects
server.transformIndexHtml, the scope of impact may be higher to also include other ad-hoc calls toserver.transformIndexHtmlfrom outside of Vite's own codebase.My best guess at bisecting which versions are vulnerable involves the following test script
and using it I was able to narrow down to #13581. If this is correct, then vulnerable Vite versions are 4.4.0-beta.2 and higher (which includes 4.4.0).
References