Game Rules


In each lab (every week), you are asked to solve a set of challenges (typically 10 challenges except for the first two weeks). In each challenge, you have to submit three things, namely, a flag, the exploit, and its write-up via scoreboard (On-site / OMSCS / OCY): the flag you got from the challenge, the exploit that you wrote, and the write-up that summarizes how you formulated the exploit (see below).

A flag is a 512-byte hex string (like below) and you can find it in /proc/flag in the assigned VM.

$ cat /proc/flag

Your job is to read this flag by exploiting the distributed challenges.

Taking actions #1 Registration

  1. Register your account and receive an api-key
  • Visit the submission site: On-site / OMSCS / OCY. You will use the registration menu.
  • Input your username (preferably your real name), e-mail address (we only accept account) and click the Email api-key button.
  • Once you succeed, you will receive an email including your API-key. You will use this api-key when you login to the course website.
  1. Login to your account
  • Go back to the submission site. You will use the Login menu.
  • Input your received api-key and click the Submit api-key button.
  1. Now, you can connect to the server and begin your lab challenges. You can find ssh details for a particular lab on the submission site.
# login to one of CTF servers
** Refer to Canvas for ssh information! **
[host] $ ssh lab01@ctf_server_address

# let's start lab01!
[CTF server] $ cat README
[CTF server] $ ./bomb
  1. While solving problems you might need to write your own scripts. Feel free to create a directory inside /tmp for your files. Note that the VM would be shared with all other users so avoid using common directory names. Listing files in /tmp is not allowed. Also, please keep a backup of your files since the /tmp folder might be emptied after a certain time.
  2. Submit your solution and flag.
  • Login → Problems → Submit (Flag / Writeup)
  • You will get actual score once you submit both flag and write-ups.

Taking actions #2 (Building local environment)

Although you can solve all challenges in the remote server, it may be inconvenient because you may not be able to install your own toolbox or use restricted tools. In this case, you can build your own environment. However, you still have to read /proc/flag through the course CTF server to get a real flag.

To build your own environment:

  1. Download and install Virtualbox/Vagrant

Note: Ubuntu users may want to use the following commands to install Virtualbox and Vagrant

[host] $ sudo apt-get install virtualbox
[host] $ sudo apt-get install vagrant
  1. Download our local setup and create a vagrant box:
[host] $ wget
[host] $ tar xvzf local_setup.tar.gz
[host] $ cd local_setup
[host] $ vagrant up
  1. To do labs (lab03 and after):
# ssh into VM
[host] $ vagrant ssh

# disable ASLR (before lab05)
[vm] $ echo 0 | sudo tee /proc/sys/kernel/randomize_va_space

# enable ASLR (starting lab05)
[vm] $ echo 2 | sudo tee /proc/sys/kernel/randomize_va_space

# download labXX challenges
[vm] $ scp -r labXX@server:~/[challenge] [your_directory]

# download libc used by the server for analysis (future labs)
# 32-bit
[vm] $ scp labXX@server:/lib/i386-linux-gnu/ [your_directory]
# 64-bit
[vm] $ scp labXX@server:/lib/x86_64-linux-gnu/ [your_directory]

# tackle challenges
[vm] $ cd [your_directory_for_challenge]
[vm] $ cat README

Feel free to ask for any help on Piazza, or at the office hours if you have any trouble during the setup.

General rule

If not specified (e.g., first two weeks), we will follow the scoring rules stated below:

  • Approximately 1 tutorial and 10 challenges every week.
  • 20 points (flag) x 1.0 (write-up/exploit) = 20 points (each challenge).
  • 220 points (20 points x 11 challenges) are the maximum points, in theory.
  • Bonus: first and second bloods (i.e., fastest solvers) will get 2 and 1 bonus points, respectively for each challenge.
  • Hint: We will provide up to two hints but you will get 5% of deduction when you open the hint.
  • Late policy: 50% of the original points (only within one week past the due date).


You should submit a write-up for each exploit to get actual point.

  • Your write-up should be a normal text file (i.e., don’t use document application such as PDF or Word).
  • Your write-up should contain both simple description about how to solve the challenge and the actual exploit.
  • It is highly recommended you use Markdown for write-ups.
  • Once you submit write-up with exploit, we will validate your exploit.
  • You don’t need to submit write-up for tutorial.
1) Write-up:

In this problem, ebp and ret value are protected by gsstack. while
debugging, you can see all ebp and ret values are keep tracking and
storing somewhere. However, when you make an input large enough, you
will see that a function pointer will be overwritten. And the
overwritten value will be store in EAX and make it jump at
<main+96>. I put my shellcode as env, get the address, and put it. In
my case, the function pointer(0x08048b0a at 0xbffff654) was
overwritten. So we could learn, we could jump using the weakpoint even
though the stackshiled is working on.

2) Exploit:

  $(python -c 'print "\x90"*108+"\x90"*44+"\x87\xf8\xff\xbf"+"\x90"*50')