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Introduction:

HTML Injection (HTMLi) is a common web vulnerability where attackers inject malicious HTML code into input fields, leading to unintended rendering in emails, dashboards, or exported files. Security researcher Shivang Maurya highlights seven high-impact methods to discover HTMLi bugs—each potentially earning $100–$200 in bug bounty programs.

Learning Objectives:

• Identify vulnerable input fields in web applications.
• Execute and verify HTML Injection payloads.
• Understand mitigation techniques for developers.

You Should Know:

1. Exploiting Contact Forms

Payload:

<h1>Shivang</h1>

Steps:

1. Locate a contact form (name, email, message fields).

2. Inject the payload into the name field.

3. Submit and check the confirmation email.

1. If the email renders `
   

   Shivang

   ` as a heading, HTMLi is confirmed.

Impact: Attackers can deface emails or escalate to XSS if combined with other vulnerabilities.

2. CRM System Testing

Payload:

<marquee>Shivang</marquee>

Steps:

1. Test input fields in CRM systems (e.g., name, company, description).

2. Submit via POST request.

1. Check if the payload reflects in UI or API responses.

Developer Fix: Sanitize inputs using libraries like DOMPurify or encode output.

3. Invite User Function Exploitation

Payload:

<b>Shivang</b>

Steps:

1. Find “Invite User” or “Team Invite” features.

2. Inject payload into the name field.

1. Observe if the invite email renders bold text.

Why It Matters: Stored HTMLi can affect admin dashboards, leading to phishing risks.

4. Profile/Account Updates

Payload:

<script>alert(1)</script> <!-- Test for XSS potential -->

Steps:

1. Update profile fields (username, bio, company).

1. Check dashboards or admin panels for script execution.

Mitigation: Use CSP headers and input validation.

5. Feedback & Support Forms

Payload:

<img src="x" onerror="alert(1)">

Steps:

1. Submit a support ticket with the payload.

2. Check admin interfaces for script execution.

Risk: Unfiltered inputs in helpdesk systems can lead to stored XSS.

6. PDF/Invoice Export Vulnerabilities

Payload:

<iframe src="javascript:alert(1)"></iframe>

Steps:

1. Inject payload into exportable fields (e.g., project name).

2. Generate PDF/CSV and check for script execution.

Fix: Sanitize data before PDF rendering.

7. Email Notification Exploits

Payload:

<a href="malicious.site">Click Me</a>

Steps:

1. Inject into project/team name fields.

2. Trigger system emails and check link rendering.

Impact: Phishing attacks via legitimate-looking emails.

What Undercode Say:

• Key Takeaway 1: HTMLi is often overlooked but highly exploitable in emails and exports.
• Key Takeaway 2: Chaining HTMLi with XSS can escalate impact to account takeover.

Analysis: While HTMLi is low-severity alone, it exposes weak input sanitization, hinting at deeper flaws. Bug hunters should report it with proof of impact (e.g., defacement or phishing potential).

Prediction:

As businesses rely more on automated email systems and CRMs, HTMLi bugs will increase—especially in SaaS platforms. Future exploits may combine HTMLi with SVG injection or DOM-based XSS for wider attacks. Developers must adopt strict output encoding and CSP policies.

Final Tip: Always test with escalating payloads (e.g., `