vite allows server.fs.deny bypass via backslash on Windows

Summary

Files denied by server.fs.deny were sent if the URL ended with \ when the dev server is running 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)
• running the dev server on Windows

Details

server.fs.deny can contain patterns matching against files (by default it includes .env, .env.*, *.{crt,pem} as such patterns). These patterns were able to bypass by using a back slash(\). The root cause is that fs.readFile('/foo.png/') loads /foo.png.

PoC

npm create vite@latest
cd vite-project/
cat "secret" > .env
npm install
npm run dev
curl --request-target /.env\ http://localhost:5173