Portswigger: Exploiting XInclude to retrieve files Writeup

Lab link.

This lab has a “Check stock” feature that embeds the user input inside a server-side XML document that is subsequently parsed.

Because you don’t control the entire XML document you can’t define a DTD to launch a classic XXE attack.

To solve the lab, inject an XInclude statement to retrieve the contents of the /etc/passwd file.

XInclude is a specification for creating sub-documents in an XML document. If the system allows it, we can read the file.

<foo xmlns:xi="http://www.w3.org/2001/XInclude"><xi:include parse="text" href="file:///etc/passwd"/></foo>