Table of Contents
XML external entity injection
What is XML external entity injection?
Answer: XML external entity injection (also known as XXE) is a web security vulnerability that allows an attacker to interfere with an application’s processing of XML data. It often allows an attacker to view files on the application server filesystem and to interact with any back-end or external systems that the application itself can access.
How do XXE vulnerabilities arise?
Answer: Some applications use the XML format to transmit data between the browser and the server. Applications that do this virtually always use a standard library or platform API to process the XML data on the server. XXE vulnerabilities arise because the XML specification contains various potentially dangerous features, and standard parsers support these features even if they are not normally used by the applications.
What are the types of XXE attacks?
1: Exploiting XXE to retrieve files:
Where an external entity is defined containing the contents of a file, and returned in the application’s response.
2: Exploiting XXE to perform SSRF attacks:
Where an external entity is defined based on a URL to a back-end system.
3: Exploiting blind XXE to exfiltrate data out-of-band:
Sensitive data is transmitted from the application server to a system that the attacker controls.
4: Exploiting blind XXE to retrieve data via error messages:
Where the attacker can trigger a parsing error message containing sensitive data.
