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# TE.CL HTTP Request Smuggling Vulnerability
TE.CL HTTP Request Smuggling Vulnerability notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### HTTP Request Smuggling, Basic TE.CL Vulnerability
In this scenario, the application uses a frontal server and an internal server. The **back-end server does not support chunked encoding**, while the **front-end server only accepts GET and POST** methods. This behavior difference allows us to exploit a vulnerability of type **TE.CL**, where the front server interprets the query according to the Transfer-Encoding header, while the internal server is based on Content-Length.
#### **Lab Objective**
Inject a query into the HTTP stream so that the next **request processed by the back-end server appears to use the `GPOST`** method, which validates the lab.
#### **Notes Importantes**
* Although the lab supports HTTP/2, the technique expected is based exclusively on mechanisms specific to **HTTP/1**. The protocol should therefore be manually modified in Burp Repeater if necessary.
* Length fields can be difficult to handle properly. The **HTTP Request Smuggler** extension available in the BApp Store facilitates this task.
#### **Example Payload Exploiting TE.CL**
In this attack, the front server interprets the message in chunked mode, while the back-end server calculates the end of the query via Content-Length, allowing to enter a second query:
```http
POST / HTTP/1.1
Host: 0acf00f80484e31881442f77004300cd.web-security-academy.net
Connection: keep-alive
Transfer-Encoding: chunked
Content-Type: application/x-www-form-urlencoded
Content-Length: 4
72
GPOST / HTTP/1.1
Host: 0acf00f80484e31881442f77004300cd.web-security-academy.net
Content-Length: 20
test=test
0
```
---
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