> 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/request-smuggling/queue-poisoning-with-h2-te.md).
# Queue Poisoning with H2.TE
Queue Poisoning with H2.TE notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### Response Queue Poisoning via H2.TE Request Smuggling
* Take advantage of request smuggling vulnerability to poison the response queue.
* Use this poisoning to access the `/admin` administration panel.
* Recover the admin query (and thus its session cookie) when it connects, then delete the `carlos` user.
#### Technical Context
* The application accepts requests **HTTP/2** front-end side.
* The front-end **downgrades** these HTTP/2 requests to HTTP/1, even when the length is ambiguous.
* The attack is based on unsynchronization of type **H2.TE**:
* Sends an HTTP/2 query containing both:
* a `Transfer-Encoding: chunked` header
* a `Content-Length` header
* The connection to the back-end is **reset every 10 requests**:
* if the connection is "broken", just send a few normal requests to go back to a clean connection.
* In HTTP/2, you do not need to define `Content-Length` normally, which makes the simultaneous presence of `Transfer-Encoding` and `Content-Length` ambiguous and usable.
#### Motion for Attack
```http
POST / HTTP/2
Host: 0afc007a0423d9b980403f2c00dd00d7.web-security-academy.net
Transfer-Encoding: chunked
Content-Length: 120
0
GET / HTTP/1.1
Host: 0afc007a0423d9b980403f2c00dd00d7.web-security-academy.net
Content-Length: 12
testing=test
```
* The HTTP/2 part is seen by the front-end, which converts it to HTTP/1 for the back-end.
* Because of the ambiguity `H2.TE`, the back-end interprets the end of the request differently.
* The `GET / HTTP/1.1` line and the following are **furtively injected** as the start of the next query in the back-end line.
We **retrieve the request for poisoned admin**, which allows us to get: its **session cookie**.
---
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