Google CTF 2018 Beginners Quest Writeups

Wed, 19 Dec 2018 08:54:08 +0900

This article was machine-translated from the Japanese version.

This article is for day 19 of the CTF Advent Calendar 2018. Day 18 was mage_1868’s MortAl mage aGEnts write-up.

As a CTF beginner, I’ve been working through the Google CTF 2018 Beginners Quest, and I’m putting together the write-ups I’ve been writing in my Diary. I haven’t finished them all yet, so I’ll add the rest as soon as I solve them.

I was planning to write about the tools I used as well, but since it would get too long, I’ll save that for another time. If you have any comments, please reach out on Twitter or Mastodon.

SECCON Beginners 2018 Nagoya CTF Writeups

Sat, 24 Nov 2018 20:51:48 +0900

This article was machine-translated from the Japanese version.

7th place out of 60+N people. The problems have not been made public.

Calc

An HTML version of “Te-Keisan Extremes” from SECCON Beginners CTF 2018. However, there is no time limit for the answers.

Get the mathematical expression and POST the result. Don’t forget to set the cookie for user identification.

import urllib.request
import urllib.parse
from bs4 import BeautifulSoup
from http.cookiejar import CookieJar

url = "http://10.2.6.1:8080/index.php"

opener = urllib.request.build_opener(urllib.request.HTTPCookieProcessor(CookieJar()))
res = opener.open(url)
html = res.read().decode("utf-8")
soup = BeautifulSoup(html, "html.parser")
exp = soup.find("div").text

for _ in range(100):
    data = urllib.parse.urlencode({'answer':eval(exp)}).encode('utf-8')
    res = opener.open(url, data)
    html = res.read().decode("utf-8")
    print(html)
    soup = BeautifulSoup(html, "html.parser")
    exp = soup.find("div").text

do alert

Inject <script>alert(0)</script> into the provided form and reload.

CTF on Unigiri

Google CTF 2018 Beginners Quest Writeups

SECCON Beginners 2018 Nagoya CTF Writeups

Calc

do alert