TKCTF

This is a template for your docker image that will be used to host your CTF challenge.

Overview

Download the template from the course website and unzip it.

    $ wget https://tc.gts3.org/cs6265/2026-fall/_static/ctf-template.zip
    $ unzip ctf-template.zip

    $ cd ctf-template
    $ make help
    prepare: prepare a docker image for compilation
    build  : build the target
    dist   : build the docker image
    release: build the target, docker image and release them
    run    : run the docker container
    exploit: launch the exploit
    test   : test the docker/exploit
    submit : zip for submission

Keep in mind that the best challenge should be fun and educational. Please don't design the challenge that requires any random/pure guessing (but well-designed bruteforcing is fine).

You can replicate real security vulnerabilities, like mini-sudo or mini-heartbleed. There are a few sources that you can refer:

• https://ctftime.org/
• https://www.cvedetails.com/
• https://www.exploit-db.com/

Structure

    /NAME                : team-name:challenge-name (e.g., `staff:fmtstr`)
    /PORT                : a port number

    # all files to run your service
    /docker/Dockerfile   : Dockerfile
           /target       : target binary
           /flag         : follow this format: tkctf{please submit this flag!}

    # all files to be released to participants
    /release/README.md   : guideline
            /target      : target binary, if you want to release

    # source/exploit for your team and organizer
    /source/Dockerfile   : Dockerfile for the build environment
           /exploit.py   : exploit code
           /test.sh      : run docker, run exploit.py and print out flag
           /writeup.txt  : solution
           /src/         : source code

Workflow

1. Change the NAME file to your challenge name: teamname:challenge (e.g., staff:fmtstr)
2. Change the docker/flag file as you wish, but wrap it inside tkctf{...} (e.g., tkctf{please submit this flag!})
3. make prepare to build a docker container for the build process
4. Design your challenge under source/src/
   • All code and Makefile go to source/src/
   • See source/src/Makefile to enable/disable mitigation
   • Put README.md under release/README.md
   • make build to build the challenge
5. make dist to prepare a docker image for exploitation
6. Put an exploit to source/exploit.py (e.g., make run and make exploit)
7. Make sure everything is ready with make test
8. make release to rebuild everything and copy the target to release/
   • Check what's included in /release/
9. make submit to zip your challenge to ../<NAME>.zip, upload it to a shareable link, and submit the link through the form printed by make submit

The source code of the challenge locates in source/src/, which contains its source (fmtstr.c) and makefile (Makefile). The makefile includes various defense options you can enable (e.g., CFLAGS += -fstack-protector). Please carefully enable them as you'd like for your challenge.

Checklist for submission

1. /NAME: Team/challenge name
2. /release/README.md: Description about the challenge
3. /release/target: the target binary to release
4. /release/*: anything else you would like to make public (e.g. libc)
5. /docker/flag: Flag!
6. /source/writeup.txt: Your description on the challenge and solution
7. /source/exploit.py: Your working exploit
8. Make sure make test works!

The game day

• The organizer will run make dist to prepare the docker image
• The organizer will release /release/* via CTFd
• Your docker image will be monitored with your exploit script