Proof-of-concept for an 'invisible' JavaScript payload.
It's possible to encode JavaScript as zero-width unicode characters and have it execute on page load. This is going to make it much harder to pick out potential malware by eye because most editors don't even show these characters:
| Name | Codepoint | Character (between ][) |
Translation |
|---|---|---|---|
| ZERO WIDTH SPACE | U+200B | ][ | 0 |
| ZERO WIDTH NON-JOINER | U+200C | ][ | 1 |
| ZERO WIDTH JOINER | U+200D | ][ | |
The demo works by using these characters to encode a JavaScript payload in binary (\u200b and \u200c representing 0 and 1 and \u200d separating bytes). When the page loads, a little bit of code decodes this to ASCII and appends it to the page in the onload event handler of an img element. If you open up the code in most editors, all you will see is an empty string.
You can generate your own page with your own custom 'invisible' script using the files in /src/generator. Pipe the JavaScript you'd like to embed to the genpage.sh script like this:
echo "alert('Its free real estate!')" | bash genpage.sh > mypage.htmlYou'll obtain mypage.html which will show an alert, but try finding the alert code in the source! Now try piping a file to /src/detection/detector.py like so:
cat ../demo.html | python detector.pyImportant note: These scripts won't work on Windows because Powershell doesn't support UTF-8 output properly. You'll have to use them from another OS or a VM.
This proof-of-concept has been put together as a supplement to my blog post for the purpose of raising awareness of the dangers of copying and pasting code from the internet that might contain hidden malicious code. This research tool should not be abused, even though it can't do anything you couldn't just do using find/replace in Notepad++ and a free online ASCII to binary converter like this one.
I've done a little bit of a write-up on my blog about this to highlight why copying and pasting code from the internet isn't a great idea. If you come across code on the internet, without careful examination it's entirely possible to end up pasting 'invisble' malware into your projects.