PicoCTF 2018 Walkthrough 1-16

Writeups Aug 16, 2021

If you're new to the world of CTFs, or want some simple challenges that won't take hours of commitment to break, PicoCTF is a great starting point. The platforms challenges are short and begin from a low difficulty level - meaning even those new to information security can start here, using nothing more than Google and intuition to make a start. The challenges are divided amongst 5 domains and difficulty slowly increases are point values per challenge increase. You can attempt PicoCTF 2018 here 2018game.picoctf.com

Forensics Warmup 1 | 50pts

Download the flag.zip file.

Navigate to the Downloads folder using cd

Unzip the folder using unzip flag.zip

Use ls to prove the unzip worked. the file flag.jpg should be present.

Attempt to open the file using display flag.jpg. If this fails install the correct software using the command returned in the output.

cd ~/Downloads
unzip flag.zip
ls
sudo apt install imagemagick-6.q16
display glasg.jpg

Forensics Warmup 2 | 50pts

Download flag.png

Use file command to discover flag.png is a jpeg file

Rename file by using mv

Open file with display

file flag.png
mv flag.png flag.jpeg
display flag.jpeg

General Warmup 1 | 50pts

open GCHQ CyberChef

Select from hex to decode text as the recipe

Input '41'

Then type the output 'A' as the flag

General Warmup 2 | 50pts

Using GCHQ CyberChef again, select 'from base' and set the value to 10.

Input '27'

The output, '11011' then needs to be inserted within the standard PicoCTF flag format.

General Warmup 3 | 50pts

Open GCHQ CyberChef

Select from base and set '16', to base and set '10', as the recipe

Input '3D'

Then type the output '61' as the flag

Resources | 50pts

Simply visit the resources and read to the bottom. there will be a flag at the bottom that can be pasted over. Bonus, can you guess the language the flag is in?

Reversing Warmup 1 | 50pts

Navigate to the desired location using cd

Run the file with ./run

Reversing Warmup 2 | 50pts

Use cyberchef, setting from Base 64 to Decode Text.

Crypto Warmup 1 | 75pts

Using a  Vigenere Decoder, such as the one available on cyberchef, input the string in the input and 'thisisalilkey' as the key.

The output will be the flag.

Crypto Warmup 2 | 75pts

Using a rot13 recipe on cyberchef, input the string.

grep 1 | 75pts

first run the file command on  file. This returns that file is ASCII text, with very long lines.

Next run a grep on the file, searching for the "picoCTF" string.

The output is the flag.

file file
cat file | grep "picoCTF"

net cat | 75pts

run the nc command with the params in the solve tab.

Output is the flag.

nc 2018shell.picoctf.com 10854

HEEEEEEERE'S Johnny! | 100pts

First install John the Ripper on the local machine, by running sudo apt install john.

Next, download the shadow file from the picoCTF solve section.

Then source a copy of the rock you wordlist from github.

Then run john with the values above as parameters.

Next log into the shell using the credentials just cracked, the shell will return the flag.

sudo apt install john
john shadow -wordlist:rockyou.txt
nc 2018shell.picoctf.com 35225
root
hellokitty

strings | 100pts

Running file strings shows that the file is a binary file.

Running strings command on the strings file will display the ASCII contents of the bin file. Piping this command to a grep searching for 'picoctf' will return the flag

file strings
strings strings | grep "picoCTF"

pipe | 110pts

nc the reverse shell and pipe output to a grep search

nc 2018shell.picoctf.com 2015 | grep "picoCTF"

Inspect Me | 125pts

View the page source. part one is found in HTML, part two is found on CSS and part three in the js

Tags

Josh Caulfield

InfoSec & Data Science. Currently studying BSc in Data Science. Sec+ | CySA+ | AWS-CCP

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