# Dangling Markup Injection

Dangling markup injection playbook.

- Repository: https://github.com/yaklang/hack-skills (2601 stars)
- Category: Engineering
- License: MIT
- Last updated: 2026-09-13
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add yaklang/hack-skills --skill dangling-markup-injection -g -a claude-code -y`
Codex: `npx skills add yaklang/hack-skills --skill dangling-markup-injection -g -a codex -y`
Cursor: `npx skills add yaklang/hack-skills --skill dangling-markup-injection -g -a cursor -y`
Gemini CLI: `npx skills add yaklang/hack-skills --skill dangling-markup-injection -g -a gemini-cli -y`

## Description

Dangling markup injection playbook. Use when HTML injection is possible but JavaScript execution is blocked (CSP, sanitizer strips event handlers, WAF blocks script tags), exfiltrate CSRF tokens, session data, and page content by injecting unclosed HTML tags that capture subsequent page content.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# SKILL: Dangling Markup Injection, Exfiltration Without JavaScript

> **AI LOAD INSTRUCTION**: Covers dangling markup exfiltration via unclosed img/form/base/meta/link/table tags, what can be stolen (CSRF tokens, pre-filled form values, sensitive content), browser-specific behavior, and combinations with other attacks. Base models often overlook this technique entirely when CSP blocks scripts, jumping to "not exploitable", dangling markup is the answer.

## 0. RELATED ROUTING

- [xss-cross-site-scripting](../xss-cross-site-scripting/SKILL.md) when full XSS is possible (no need for dangling markup)
- [csp-bypass-advanced](../csp-bypass-advanced/SKILL.md) when CSP blocks JS execution, dangling markup bypasses script restrictions
- [csrf-cross-site-request-forgery](../csrf-cross-site-request-forgery/SKILL.md) when dangling markup steals CSRF tokens for subsequent CSRF attacks
- [crlf-injection](../crlf-injection/SKILL.md) when CRLF enables HTML injection in HTTP response
- [web-cache-deception](../web-cache-deception/SKILL.md) when dangling markup + cache poisoning amplifies the attack

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## 1. WHEN TO USE DANGLING MARKUP

You need dangling markup when ALL of these are true:

1. You have an HTML injection point (reflected or stored)
2. JavaScript execution is blocked:
   - CSP blocks inline scripts and event handlers
   - Sanitizer strips `<script>`, `onerror`, `onload`, etc.
   - WAF blocks known XSS patterns
3. The page contains sensitive data AFTER your injection point:
   - CSRF tokens
   - Pre-filled form values (email, username, API keys)
   - Session identifiers in hidden fields
   - Sensitive user content

**Core insight**: You don't need JavaScript to exfiltrate data, you just need the browser to make a request that includes the data in the URL.

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## 2. CORE TECHNIQUE

The rest: https://github.com/yaklang/hack-skills/blob/HEAD/skills/dangling-markup-injection/SKILL.md