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# lab-7

## Exploiting XInclude to Retrieve Files

**Difficulty:** Practitioner

### Lab Description

This lab has a "Check stock" feature that embeds user input inside a server-side XML document, which is subsequently parsed. Because the full XML document isn't user-controlled, a classic XXE attack (which requires defining a `DOCTYPE`/DTD) isn't possible here.

**Objective:** Inject an XInclude statement to retrieve the contents of the `/etc/passwd` file.

### Solution

**Step 1 — Identify the constraint**

In this lab there's no visible, fully-controllable XML structure to manipulate directly — the input goes into a single parameter (`productId`) that the backend embeds into a larger, server-controlled SOAP/XML document. Since the `DOCTYPE` declaration must appear before the root element and the attacker doesn't control the full document, a standard external entity injection won't work.

**Step 2 — Use XInclude instead of a DTD**

XInclude is a separate XML feature that lets a single element pull in external content without requiring a `DOCTYPE` declaration — making it usable even when only a single parameter value is controlled.

**Step 3 — Inject the XInclude payload**

In the `productId` parameter (or any other vulnerable input field embedded into server-side XML), submit:

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

This tells the parser to process the `xi:include` directive and pull in the contents of `/etc/passwd` as plain text at that location in the document.

**Step 4 — Confirm the result**

Send the request. The response reflects the contents of `/etc/passwd` in place of the original parameter value, confirming the file read.

### Conclusion

XInclude attacks expand the XXE attack surface beyond places where a full XML document — and therefore a `DOCTYPE`/DTD — is directly controllable. Any input that ends up embedded inside a server-side XML document is a potential injection point, even without DTD-based payloads.


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