Summary

server.fs check was not enforced to the fetchModule method that is exposed in Vite dev server's WebSocket.

Impact

Only apps that match the following conditions are affected:

- explicitly exposes the Vite dev server to the network (using --host or server.host config option) - WebSocket is not disabled by server.ws: false

Arbitrary files on the server (development machine, CI environment, container, etc.) can be exposed.

Details

If it is possible to connect to the Vite dev server’s WebSocket without an Origin header, an attacker can invoke fetchModule via the custom WebSocket event vite:invoke and combine file://... with ?raw (or ?inline) to retrieve the contents of arbitrary files on the server as a JavaScript string (e.g., export default "...").

The access control enforced in the HTTP request path (such as server.fs.allow) is not applied to this WebSocket-based execution path.

PoC

1. Start the dev server on the target Example (used during validation with this repository): bash pnpm -C playground/alias exec vite --host 0.0.0.0 --port 5173

2. Confirm that access is blocked via the HTTP path (example: arbitrary file) bash curl -i 'http://localhost:5173/@fs/etc/passwd?raw' Result: 403 Restricted (outside the allow list) <img width="3898" height="1014" alt="image" src="https://github.com/user-attachments/assets/f6593377-549c-45d7-b562-5c19833438af" />

3. Confirm that the same file can be retrieved via the WebSocket path By connecting to the HMR WebSocket without an Origin header and sending a vite:invoke request that calls fetchModule with a file://... URL and ?raw, the file contents are returned as a JavaScript module. <img width="1049" height="296" alt="image" src="https://github.com/user-attachments/assets/af969f7b-d34e-4af4-8adb-5e2b83b31972" /> <img width="1382" height="955" alt="image" src="https://github.com/user-attachments/assets/6a230d2e-197a-4c9c-b373-d0129756d5d7" />

Summary

Any files ending with .map even out side the project can be returned to the browser.

Impact

Only apps that match the following conditions are affected:

- explicitly exposes the Vite dev server to the network (using --host or server.host config option) - have a sensitive content in files ending with .map and the path is predictable

Details

In Vite v7.3.1, the dev server’s handling of .map requests for optimized dependencies resolves file paths and calls readFile without restricting ../ segments in the URL. As a result, it is possible to bypass the server.fs.strict allow list and retrieve .map files located outside the project root, provided they can be parsed as valid source map JSON.

PoC 1. Create a minimal PoC sourcemap outside the project root bash cat > /tmp/poc.map <<'EOF' {"version":3,"file":"x.js","sources":[],"names":[],"mappings":""} EOF 2. Start the Vite dev server (example) bash pnpm -C playground/fs-serve dev --host 127.0.0.1 --port 18080 3. Confirm that direct /@fs access is blocked by strict (returns 403) <img width="4004" height="1038" alt="image" src="https://github.com/user-attachments/assets/15a859a8-1dc6-4105-8d58-80527c0dd9ab" /> 4. Inject ../ segments under the optimized deps .map URL prefix to reach /tmp/poc.map <img width="2790" height="846" alt="image" src="https://github.com/user-attachments/assets/5d02957d-2e6a-4c45-9819-3f024e0e81f2" />

Summary

The contents of files that are specified by server.fs.deny can be returned to the browser.

Impact

Only apps that match the following conditions are affected:

- explicitly exposes the Vite dev server to the network (using --host or server.host config option) - the sensitive file exists in the allowed directories specified by server.fs.allow - the sensitive file is denied with a pattern that matches a file by server.fs.deny

Details

On the Vite dev server, files that should be blocked by server.fs.deny (e.g., .env, .crt) can be retrieved with HTTP 200 responses when query parameters such as ?raw, ?import&raw, or ?import&url&inline are appended.

PoC

1. Start the dev server: pnpm exec vite root --host 127.0.0.1 --port 5175 --strictPort 2. Confirm that server.fs.deny is enforced (expect 403): curl -i http://127.0.0.1:5175/src/.env | head -n 20 <img width="3944" height="1092" alt="image" src="https://github.com/user-attachments/assets/ecb9f2e0-e08f-4ac7-b194-e0f988c4cd4f" /> 3. Confirm that the same files can be retrieved with query parameters (expect 200): <img width="2014" height="373" alt="image" src="https://github.com/user-attachments/assets/76bc2a6a-44f4-4161-ae47-eab5ae0c04a8" />

Summary

The contents of files that are specified by server.fs.deny can be returned to the browser on Windows.

Impact

Only apps that match the following conditions are affected:

- explicitly exposes the Vite dev server to the network (using --host or server.host config option) - the sensitive file exists in the allowed directories specified by server.fs.allow - either of: - the sensitive file exists in an NTFS volume - the dev server is running on Windows and the sensitive file exists in a volume that 8.3 short name generation is enabled (it is enabled by default on system volumes)

Details

Vite’s dev server denies direct access to sensitive files through server.fs.deny, including entries such as .env, .env., and .{crt,pem}. However, on Windows, the deny logic does not correctly normalize NTFS ADS path forms before access checks are applied. Because of this, requests such as /.env::$DATA?raw are treated as allowed paths, while Windows resolves them to the original file's default data stream.

Similar to that, Windows allows accessing a file using a different name with the 8.3 short name compatibility feature. Vite did not reject accessing files via them.

PoC bash $ npm create vite@latest $ cd vite-project/ $ npm install $ npm run dev Access via browser at http://localhost:5173/.env::$DATA?raw <img width="388" height="129" alt="deecc1315123883cfd0f9c26a002845a" src="https://github.com/user-attachments/assets/895c6012-4e2e-4a35-babb-69bbf3ee7170" />

Example expected result: - /.env::$DATA?raw returns the contents of .env - /tls.pem::$DATA?raw returns the contents of tls.pem

Summary Files starting with the same name with the public directory were served bypassing the server.fs settings.

Impact Only apps that match the following conditions are affected:

- explicitly exposes the Vite dev server to the network (using --host or server.host config option) - uses the public directory feature (enabled by default) - a symlink exists in the public directory

Details The servePublicMiddleware function is in charge of serving public files from the server. It returns the viteServePublicMiddleware function which runs the needed tests and serves the page. The viteServePublicMiddleware function checks if the publicFiles variable is defined, and then uses it to determine if the requested page is public. In the case that the publicFiles is undefined, the code will treat the requested page as a public page, and go on with the serving function. publicFiles may be undefined if there is a symbolic link anywhere inside the public directory. In that case, every requested page will be passed to the public serving function. The serving function is based on the sirv library. Vite patches the library to add the possibility to test loading access to pages, but when the public page middleware disables this functionality since public pages are meant to be available always, regardless of whether they are in the allow or deny list.

In the case of public pages, the serving function is provided with the path to the public directory as a root directory. The code of the sirv library uses the join function to get the full path to the requested file. For example, if the public directory is "/www/public", and the requested file is "myfile", the code will join them to the string "/www/public/myfile". The code will then pass this string to the normalize function. Afterwards, the code will use the string's startsWith function to determine whether the created path is within the given directory or not. Only if it is, it will be served.

Since sirv trims the trailing slash of the public directory, the string's startsWith function may return true even if the created path is not within the public directory. For example, if the server's root is at "/www", and the public directory is at "/www/p", if the created path will be "/www/private.txt", the startsWith function will still return true, because the string "/www/private.txt" starts with  "/www/p". To achieve this, the attacker will use ".." to ask for the file "../private.txt". The code will then join it to the "/www/p" string, and will receive "/www/p/../private.txt". Then, the normalize function will return "/www/private.txt", which will then be passed to the startsWith function, which will return true, and the processing of the page will continue without checking the deny list (since this is the public directory middleware which doesn't check that).

PoC Execute the following shell commands:

npm create vite@latest cd vite-project/ mkdir p cd p ln -s a b cd .. echo 'import path from "node:path"; import { defineConfig } from "vite"; export default defineConfig({publicDir: path.resolve(dirname, "p/"), server: {fs: {deny: [path.resolve(dirname, "private.txt")]}}})' > vite.config.js echo "secret" > private.txt npm install npm run dev

Then, in a different shell, run the following command:

curl -v --path-as-is 'http://localhost:5173/private.txt'

You will receive a 403 HTTP Response,  because private.txt is denied.

Now in the same shell run the following command:

curl -v --path-as-is 'http://localhost:5173/../private.txt'

You will receive the contents of private.txt.

Related links - https://github.com/lukeed/sirv/commit/f0113f3f8266328d804ee808f763a3c11f8997eb

Summary Any HTML files on the machine were served regardless of the server.fs settings.

Impact

Only apps that match the following conditions are affected:

- explicitly exposes the Vite dev server to the network (using --host or server.host config option) - appType: 'spa' (default) or appType: 'mpa' is used

This vulnerability also affects the preview server. The preview server allowed HTML files not under the output directory to be served.

Details The serveStaticMiddleware function is in charge of serving static files from the server. It returns the viteServeStaticMiddleware function which runs the needed tests and serves the page. The viteServeStaticMiddleware function checks if the extension of the requested file is ".html". If so, it doesn't serve the page. Instead, the server will go on to the next middlewares, in this case htmlFallbackMiddleware, and then to indexHtmlMiddleware. These middlewares don't perform any test against allow or deny rules, and they don't make sure that the accessed file is in the root directory of the server. They just find the file and send back its contents to the client.

PoC Execute the following shell commands:

npm create vite@latest cd vite-project/ echo "secret" > /tmp/secret.html npm install npm run dev

Then, in a different shell, run the following command:

curl -v --path-as-is 'http://localhost:5173/../../../../../../../../../../../tmp/secret.html'

The contents of /tmp/secret.html will be returned.

This will also work for HTML files that are in the root directory of the project, but are in the deny list (or not in the allow list). Test that by stopping the running server (CTRL+C), and running the following commands in the server's shell:

echo 'import path from "node:path"; import { defineConfig } from "vite"; export default defineConfig({server: {fs: {deny: [path.resolve(dirname, "secretfiles/")]}}})' > vite.config.js mkdir secretfiles echo "secret txt" > secretfiles/secret.txt echo "secret html" > secretfiles/secret.html npm run dev

Then, in a different shell, run the following command:

curl -v --path-as-is 'http://localhost:5173/secretfiles/secret.txt'

You will receive a 403 HTTP Response,  because everything in the secretfiles directory is denied.

Now in the same shell run the following command:

curl -v --path-as-is 'http://localhost:5173/secretfiles/secret.html'

You will receive the contents of secretfiles/secret.html.