Vite: First 4 bytes of files outside of `server.fs` setting is exposed by `?vite-wasm-instance`

### Summary The first 4 bytes of files outside of `server.fs` setting can be returned to the browser by a request containing `?vite-wasm-instance`. ### Impact Only apps that match one of the following conditions are affected: - explicitly expose the Vite dev server to the network using `--host` or the [`server.host`](https://vite.dev/config/server-options#server-host) option - there's a file that has a sensitive information in **the first 4 bytes** - uses Node.js or Deno to run Vite (if Bun is used, it is not affected) ### Details Requests containing the `?vite-wasm-instance` query are handled by the internal Wasm plugin's `load` hook. The hook removes the query and reads the resulting path directly from disk, but the `server.fs` checks were not applied. After reading the file, Vite attempts to parse it as WebAssembly. When that parse fails, Node and deno throws an error that contains the first 4 bytes of the file. ### PoC Create a denied file and start an affected Vite dev server: ```bash echo 'SECRET_KEY=abc123\n' > .env npm run dev curl 'http://localhost:5173/.env?vite-wasm-instance' ``` This will show ``` Failed to parse WASM file "<root>/.env": WebAssembly.compile(): expected magic word 00 61 73 6d, found 53 45 43 52 @+0 ```

Source published

21 Oct 2026 16:47:15 UTC

Source modified

21 Oct 2026 17:00:07 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

Publisher rating · MODERATE