Markdown

Markdown is an easy to use markup language used in the Github README for example

Syntax

Markdown is a standard for text markup. It allows you to make text bold, italic, and in all kinds of different styles. It uses special characters around certain text to apply markup to it. Often markdown is used in text editors like on GitHub README.md files or Discord messages. Then the files are converted to another language like HTML with CSS or PDF to actually show the Here are the rules:

Markdown Cheat Sheet | Markdown Guide

A cheatsheet explaining all of the Markdown syntax

Element	Markdown Syntax
Heading	# H1 ## H2 ### H3
Bold	**bold text**
Italic	*italicized text*
	> blockquote
First item Second item Third item	1. First item 2. Second item 3. Third item
First item Second item Third item	- First item - Second item - Third item
code	`code`
	---
Link	[title](https://www.example.com)
	

Advanced Syntax

Syntax Description Header Title Paragraph Text	| Syntax | Description | | ----------- | ----------- | | Header | Title | | Paragraph | Text |
{ "firstName": "John", "lastName": "Smith", "age": 25 }	```json { "firstName": "John", "lastName": "Smith", "age": 25 } ```
Strikethrough	~~strikethrough~~
Checklist Item 2 Item 3	- [x] Write the press release - [ ] Update the website - [ ] Contact the media
Emoji! 😀	Emoji! :grinning:

Markdown XSS

Markdown often gets compiled to HTML to be styled with CSS later. When converting something to HTML you need to make sure attackers can't inject arbitrary HTML, like <script> tags. Another idea is a javascript: URL in links so JavaScript code is executed when clicked. You can find a lot of Markdown XSS payloads in the following list:

Markdown-XSS-Payloads/Markdown-XSS-Payloads.txt at master · cujanovic/Markdown-XSS-PayloadsGitHub

List of Markdown XSS payloads

To fuzz for and create your own payloads, read the following article where they explore an idea for different nested parsers that can mutate into XSS:

Fuzzing for XSS via nested parsers conditionPT SWARM

A methodology for finding Markdown XSS parser vulnerabilities in custom implementations