Xxe

Comprehensive XXE Guide A practitioner’s reference for XML External Entity injection — fundamentals, parser quirks, in-band and out-of-band exfiltration, parameter entity chains, file-format vectors, real-world CVEs, tooling, and hardening. Compiled from 41 research sources. Table of Contents Fundamentals Attack Surface & Entry Points Classic In-Band XXE Blind XXE via External DTD Error-Based XXE Parameter Entities & Local DTD Chains XXE → SSRF Pivoting XXE → File Read & Information Disclosure XXE → RCE Parser-Specific Behaviors XML File-Format Vectors WAF & Filter Bypasses Denial of Service Real-World CVEs & Chains Tooling Detection & Prevention Payload Quick Reference 1. Fundamentals XXE (XML External Entity) injection occurs when an XML parser processes attacker-controlled input with DTD (Document Type Definition) and external entity resolution enabled. The parser treats SYSTEM identifiers as URIs, fetching and substituting their content into the document — yielding file read, SSRF, blind exfiltration, DoS, and in some stacks RCE. ...

XML External Entity (XXE) injection exploits applications that parse XML input without disabling external entity resolution. If the XML parser is misconfigured (which many are by default), an attacker can define custom entities that read local files, make network requests, or cause denial of service. These payloads are for authorized security testing only. What is XXE? When an XML parser processes a document, it can resolve entities defined in the DOCTYPE declaration. External entities use the SYSTEM keyword to reference files or URLs. If the parser resolves these without restriction, the attacker controls what the server reads and where it sends data. ...