CSAWCTF_2017: Orange V1

Category: Web Points: 100 Description:

I wrote a little proxy program in NodeJS for my poems folder. Everyone wants to read flag.txt but I like it too much to share. http://web.chal.csaw.io:7311/?path=orange.txt

Write-up

This is a challenge on directory transversal attacks, with the focus on encoding the payload such that attacking it requires a double-encoded payload.

Our original attempt at http://web.chal.csaw.io:7311/?path=../ immediately responded with WHOA THATS BANNED!!!!. This led me to believing that .. is banned. So, to bypass this, all we have to do is double encode the . to %252e. Navigating to http://web.chal.csaw.io:7311/?path=%252e%252e/flag.txt gives us the flag.

Therefore, the flag is flag{thank_you_based_orange_for_this_ctf_challenge}.

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