# HTML Injection Testing

Should be used when the user asks to "test for HTML injection", "inject HTML into web...

- Repository: https://github.com/zebbern/claude-code-guide (4691 stars)
- Category: Testing
- License: MIT
- Last updated: 2026-11-01
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add zebbern/claude-code-guide --skill html-injection-testing -g -a claude-code -y`
Codex: `npx skills add zebbern/claude-code-guide --skill html-injection-testing -g -a codex -y`
Cursor: `npx skills add zebbern/claude-code-guide --skill html-injection-testing -g -a cursor -y`
Gemini CLI: `npx skills add zebbern/claude-code-guide --skill html-injection-testing -g -a gemini-cli -y`

## Description

This skill should be used when the user asks to "test for HTML injection", "inject HTML into web pages", "perform HTML injection attacks", "deface web applications", or "test content injection vulnerabilities". It provides comprehensive HTML injection attack techniques and testing methodologies.

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

# HTML Injection Testing

## Purpose

Identify and exploit HTML injection vulnerabilities that allow attackers to inject malicious HTML content into web applications. This vulnerability enables attackers to modify page appearance, create phishing pages, and steal user credentials through injected forms.

## Prerequisites

### Required Tools
- Web browser with developer tools
- Burp Suite or OWASP ZAP
- Tamper Data or similar proxy
- cURL for testing payloads

### Required Knowledge
- HTML fundamentals
- HTTP request/response structure
- Web application input handling
- Difference between HTML injection and XSS

## Outputs and Deliverables

1. **Vulnerability Report** - Identified injection points
2. **Exploitation Proof** - Demonstrated content manipulation
3. **Impact Assessment** - Potential phishing and defacement risks
4. **Remediation Guidance** - Input validation recommendations

## Core Workflow

### Phase 1: Understanding HTML Injection

HTML injection occurs when user input is reflected in web pages without proper sanitization:

```html
<!-- Vulnerable code example -->
<div>
    Welcome, <?php echo $_GET['name']; ?>
</div>

<!-- Attack input -->
?name=<h1>Injected Content</h1>

<!-- Rendered output -->
<div>
    Welcome, <h1>Injected Content</h1>
</div>
```

Key differences from XSS:
- HTML injection: Only HTML tags are rendered
- XSS: JavaScript code is executed
- HTML injection is often stepping stone to XSS

Attack goals:
- Modify website appearance (defacement)
- Create fake login forms (phishing)
- Inject malicious links
- Display misleading content

### Phase 2: Identifying Injection Points

Map application for potential injection surfaces:

```
1. Search bars and search results
2. Comment sections
3. User profile fields
4. Contact forms and feedback
5. Registration forms
6. URL parameters reflected on page
7. Error messages
8. Page titles and headers
9. Hidden form fields
10. Cookie values reflected on page
```

The rest: https://github.com/zebbern/claude-code-guide/blob/HEAD/skills/html-injection-testing/SKILL.md