Node.js third-party modules: [simple-server] HTML with iframe element can be used as filename, which might lead to load and execute malicious JavaScript

ID H1:309641
Type hackerone
Reporter bl4de
Modified 2018-03-01T23:04:03


Hi Guys,

simple-server allows to embed HTML in file names, which (in certain conditions) might lead to execute malicious JavaScript. This is caused by outdated version of connect framework.


Simple Server allows you to easily get a node.js static file server up and running anywhere anytime.


This issue is exactly the same I've reported for anywhere module ( The problem is outdated connect framework (2.10.0) with obsolete middleware used to display content of the directory as HTML.

This is the code which allows to embed HTML in file names and execute attack described in PoC (/node_modules/connect/lib/middleware/directory.js, lines 192-197):


return '<li><a href="'
  + utils.normalizeSlashes(normalize(path.join('/')))
  + '" class="'
  + classes.join(' ') + '"'
  + ' title="' + file + '">'
  + icon + file + '</a></li>';


As you can see, file is output directly into HTML without any sanitization.

Now, take a look how the same fragment of code looks in serve-index middleware, introduced in place of old middlewares like directory.js above, and used in current Connect and Express frameworks (

javascript return '<li><a href="' + escapeHtml(normalizeSlashes(normalize(path.join('/')))) + '" class="' + escapeHtml(classes.join(' ')) + '"' + ' title="' + escapeHtml( + '">' + '<span class="name">' + escapeHtml( + '</span>' + '<span class="size">' + escapeHtml(size) + '</span>' + '<span class="date">' + escapeHtml(date) + '</span>' + '</a></li>';

All output data is sanitized with escapeHtml() which sanitizes HTML before is send to browser.

I think this is the problem of all older npm modules using old versions of Connect middlewares like directory.js.

PoC - Steps To Reproduce:

In the directory which will be served via simple-server, create file with following name:

"><iframe src="malware_frame.html">

Then, HTML file with following content have to be saved in the same directory as file with the name changed:

``` <html>

<head> <meta charset="utf8" /> <title>Frame embeded with malware :P</title> </head>

<body> <p>iframe element with malicious code</p> <script type="text/javascript" src="malware.js"></script> </body>

</html> ```

An src attribute value I've used here is just for PoC purpose, this can be any external url. On my local machine, malware.js has following content:

alert('Uh oh, I am very bad malware!')

Run simple-server`` in directory where both file with filename changed andmalware_frame.html``` are saved:

$ ./node_modules/simple-server/bin/simple-server.js ./ 8080 Simple-Server listening to http://:::8080/ with directory /Users/bl4de/playground/node_bugbounty_playground

and open in the browser, you can see JavaScript from malware.js is executed.

Supporting Material/References:

Configuration I've used to find this vulnerability:

  • macOS HighSierra 10.13.3
  • node 8.9.3
  • npm 5.5.1
  • curl 7.54.0

Wrap up

I hope this report will help to keep Node ecosystem more safe. If you have any questions about any details of this finding, please let me know in comment.

Thank you


Rafal 'bl4de' Janicki


Exploitation of this vulnerability in the wild might be hard, however it's not impossible and it depends only on attacker's skills to get into directory on the server, where simple-server is used to serve static content.