Solution

This level is basically a brute-force over a 5 chars MD5 hash. We get the hash from the source code - it is 155fb95d04287b757c996d77b5ea51f7, and with a quick search online, we get the corresponding plain text - rlTf6.

There are lots of online services to crack md5, and there’s also Project RainbowCrack which uses the Time-Memory trade-off. After getting the plain text we can get to the shell:

vortex5@melissa:/vortex$ ./vortex5
Password: 
..
You got the right password, congrats!
$ cat /etc/vortex_pass/vortex6
*****