Self Notes: Web Security Academy HTTP Request Smuggling Lab 10

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Lab 10 can be found here

This was quite an interesting Lab, first, I couldn't follow my normal procedure of posting while I solve the lab, more so, I failed to solve the lab without a hint. This lab, similar to the previous lab had a CL-TE server pair, the task is to poison the Front-end server cache so that normal users request to the cache get served our exploit. What made this lab different really was just that we have to find an endpoint which returns a redirect response where the Location header was an absolute URL. To the best of my knowledge, there is only one such endpoint, which perhaps was the reason I couldn't find it easily:


The 'next post' endpoint responds with a redirect with an absolute URL:


Well, the general idea is that we need to smuggle a request that will induce a redirect to an exploit server we control, this redirect response will then get cached by the Front-end server, so a legitimate user request will get redirected to our exploit server during a cache-hit, below is the smuggling request:


When the normal request is processed by the server the smuggled request will be left on the back-end socket, we will then request an endpoint which gets cached by the front-end server:


Using the above endpoint is quite convenient since it serves a javascript file, we copy the content of the js file and add a little juice to it. The server response when the above request gets processed:


when the lab user makes a request, the front-end server responds with a redirect, the browser follows and our exploit gets executed:



Lab Solved.

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