Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
What I've Learned Writing CTF Challenges
Search
vito
February 11, 2017
Programming
0
150
What I've Learned Writing CTF Challenges
BSides Tampa, 2/11/2017
vito
February 11, 2017
Tweet
Share
More Decks by vito
See All by vito
Modernizing SQL Injection CTF Challenges
vito
0
130
Raw Water: Quenching Your Thirst for SQL Injection
vito
0
71
Lessons Learned from Five Years of Building Capture the Flag
vito
0
490
Capture the Flag: An Owner's Manual
vito
0
90
Building DEF CON CTF with Ruby
vito
0
600
Other Decks in Programming
See All in Programming
テストから始めるAgentic Coding 〜Claude Codeと共に行うTDD〜 / Agentic Coding starts with testing
rkaga
16
5.8k
階層化自動テストで開発に機動力を
ickx
1
370
はじめてのWeb API体験 ー 飲食店検索アプリを作ろうー
akinko_0915
0
160
構文解析器入門
ydah
7
1.7k
AIともっと楽するE2Eテスト
myohei
9
3.1k
Porting a visionOS App to Android XR
akkeylab
0
880
新メンバーも今日から大活躍!SREが支えるスケールし続ける組織のオンボーディング
honmarkhunt
5
9k
High-Level Programming Languages in AI Era -Human Thought and Mind-
hayat01sh1da
PRO
0
910
ペアプロ × 生成AI 現場での実践と課題について / generative-ai-in-pair-programming
codmoninc
2
22k
初学者でも今すぐできる、Claude Codeの生産性を10倍上げるTips
s4yuba
16
13k
チームで開発し事業を加速するための"良い"設計の考え方 @ サポーターズCoLab 2025-07-08
agatan
1
480
ソフトウェア品質を数字で捉える技術。事業成長を支えるシステム品質の マネジメント
takuya542
2
16k
Featured
See All Featured
Building Flexible Design Systems
yeseniaperezcruz
328
39k
Refactoring Trust on Your Teams (GOTO; Chicago 2020)
rmw
34
3.1k
Imperfection Machines: The Place of Print at Facebook
scottboms
267
13k
RailsConf 2023
tenderlove
30
1.2k
Learning to Love Humans: Emotional Interface Design
aarron
273
40k
Speed Design
sergeychernyshev
32
1k
Fireside Chat
paigeccino
37
3.5k
The Pragmatic Product Professional
lauravandoore
35
6.8k
The Straight Up "How To Draw Better" Workshop
denniskardys
235
140k
Optimising Largest Contentful Paint
csswizardry
37
3.3k
GitHub's CSS Performance
jonrohan
1031
460k
The Web Performance Landscape in 2024 [PerfNow 2024]
tammyeverts
8
700
Transcript
What I’ve Learned Writing CTF Challenges Vito Genovese BSides Tampa
February 11, 2017
What is CTF?
What is CTF?
Jeopardy Style
Attack-Defense
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
CGC Jargon • Cyber Reasoning System • Proof of Vulnerability
• Replacement Binary • Challenge Binary
BSTies http://bsties.notmalware.ru
CTF Challenges Teams attack it
CTF Challenges Protects something of in-game value
CTF Challenges Ideally: known solvable
CTF Challenges Also ideally: appropriately tricky
None
None
Solving 'em • Correct side of an if statement •
Cracking a code • Using SQL injection to trick a database • Stealing the garbage file from the Gibson
Actually Building One
None
Original Goal
Original Goal
• Given same STDIN • Same STDOUT • Same clock
cycles • Same syscalls
https://xkcd.com/1319/
Why Automate?
None
Thousand Cuts
Thousand Cuts
Thousand Cuts
Actually Building It
Start the First One 1. Set up CGC service-template 2.
Test not-crashing 3. Make binary that doesn’t crash 4. Test crashing 5. Make binary that crashes
First One's Done • Ruby script to spit out 334
binaries • Vary buffer sizes • Vary stack cookie • Python script running game flow
First Set's Done Figure out how to make second and
third sets
Second Set Python script to add stuff to source code
Third Set Python script to rearrange source code
All Sets Done Test the difficulty
Integration Testing With Gyno • Finds a bug in like
30s • Fixing the bug took 30m • (fixing the bug a week prior would've taken 5m)
More Integration Testing kind of weird
easy-prasky • single binary • Baby’s First category • Separate
CRS work from first stab at CGCEF • Hacked to be first in 334 cuts
Deployment • Determine ops requirements • CGC kernel • Python
installed • Open port
Deployment Puppetize it!
Deployment
Running it just kinda worked (once teams Got It)
CTF Challenge Process 1.Idea 2.Build 3.Test
CTF Challenge Framework • Configuration • Build • Testing •
Deployment
CTF Challenge Framework CGC service-template
CTF Challenge Deployment put it on a server lol
It's Just Software
Software Goals Useful Usable Reliable
Useful for Competition Separate teams that solve it from teams
that don't Prefer strong correlation with finals ranking
Useful for Education Teach new players something Get players over
a hang-up
Usable Intended difficulty only Minimize corner cases Unintended vulnerabilities?
Reliable Remain vulnerable
Reliability is Hard Players like to attack Players like to
brute Players like to complain
Reliability is Hard
Reliability is Demanding
Reliability is Expensive If you want it to be
Reliability is Cheap Build software that can be run reliably
Twelve Factor App • VIII. Concurrency • Scale out via
the process model • IX. Disposability • Maximize robustness with fast startup and graceful shutdown
Twelve Factor Challenges • Limit global state • Process per
connection • xinetd ftw • Make adding resources cheap
Adding Resources Automate!
Operations Automation Puppet or Chef for server provisioning
Operations Automation Docker is slow to spin up RunC is
fast
Shared State • Process per connection not always feasible •
Sandwich challenges in 2014 • JRuby & Celluloid slow to start • State still per connection
Shared State • Global state and web challenges • Persisted
XSS • Tricking a global database
Waiting For Your Touch • 2015 web challenge • /r/thebutton
knockoff • JRuby, Rails, websockets, postgres
Waiting For Your Touch
Waiting For The Challenge Slow when not slow 500s Thankfully
during the day
Waiting For Your Touch 1. Took it down 2. Opened
replacement challenge 3. Debugged for an hour
Debugging For Your Touch 4. Leaked and exhausted postgres connections
5. Fixed leak 6. Allocated more connections
Waiting For My Fix 7. Took an hour 8. Gyno
forced a fifteen minute cool-down between "is it fixed" and "it is fixed" 9. Reopened
Most Important Part People are the most important
Respect People • Respect for yourself • Respect for your
team • Respect for players
Respect for Yourself
Respect for Your Team
Respect for Your Team
Respect for Your team Make services easy to keep running
Document!
Respect for Your Team Provide easy to run smoke tests
"Is this exploitable?" should be a one-liner that spits out the flag
Respect for Players
Respect for Players
Respect for Players
Respect for Players
Building Challenges is Software Development Useful Usable Reliable
Reliability Imposes Constraints Limit state Limit dependencies Automate
Respect Is Fundamental Self Team Players
Thanks! Vito Genovese
[email protected]
@vito_lbs GPG B07D616143CAA77B https://legitbs.net @legitbs_ctf