Hack You CTF 2012 - HugeCaptcha (PPC100)

less than 1 minute read

PPC100 is a puzzle that requires some degree of scripting. To obtain the flag, we have to add up the two large numbers given and submit the result through POST within an extremely short time limit.

The exploit is as follows (solve_ppc100.py):

import requests, re

p1 = re.compile("(d+) + (d+)")
p2 = re.compile("name='trueanswer' value='(w+)'")
r = requests.get("http://misteryou.ru/ppc100/")

res1 = p1.search(r.text)
n1 = res1.group(1)
n2 = res1.group(2)
ans = int(n1) + int(n2)

res2 = p2.search(r.text)
ta = res2.group(1)

payload = {'captchatype': 'hugecaptcha', 'trueanswer': ta, 'answer': str(ans)}
r2 = requests.post("http://misteryou.ru/ppc100/", data=payload)

p3 = re.compile("(d{7})")
secret = "".join(chr(int(i,2)) for i in p3.findall(r2.text))

print secret

Executing the python script:

[email protected]:~/hackyou/ppc100$ python solve_ppc100.py
killallhumans
[email protected]:~/hackyou/ppc100$

Flag: killallhumans

Leave a Comment