CrossCTF_2018: Skipping Rope

Category: Pwn Points: 975 Description:

How high and how fast can you go on the skipping rope? nc ctf.pwn.sg 1501 Creator - amon (@nn_amon)

Write-up

A rather interesting take on a shellcode challenge, involving the need to break the shellcode up into sections of 6 bytes long and using relative jumps to hop all over the place. After a bit of tinkering, I finally managed to split the shellcode up nicely in Python,

It is important to note that because you are splitting the instructions up into chunks of 2-4 bytes, you need to fill up the remaining spaces with NOP or 0x90.

# ./solve.py 
[+] Opening connection to ctf.pwn.sg on port 1501: Done
[+] CrossCTF{With_a_hip_hop_the_hippie_to_the_hippie}
[*] Closed connection to ctf.pwn.sg port 1501

Therefore, the flag is CrossCTF{With_a_hip_hop_the_hippie_to_the_hippie}

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