Lessons Learned from Five Years of Building Capture the Flag

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Lessons Learned from Five Years of Building Capture the Flag Vito Genovese SECCON 2017 Feb. 18, 2018

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Good Morning!

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Capture the Flag "CTF"

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DEF CON

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1996 ﬁrst game

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2000 formalized how it was run

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2002-2004 ghettohackers

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2005-2008 Kenshoto

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2009-2012 ddtek

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2013-2017 Legitimate Business Syndicate

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2018-? Order of the Overﬂow

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Two Distinct Formats

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Jeopardy Style Scoreboard

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Jeopardy Style Prompt

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Jeopardy Style Solving

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Jeopardy Style Points

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Jeopardy Style DEF CON CTF Quals

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Photo: robbje @ Eat Speep Pwn Repeat

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asby From SHA2017 CTF

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asby Get ﬁle

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asby Identify Windows STDIO .exe

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asby Determine goal

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asby Guess the correct input

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asby •Reverse engineer a Windows binary •Guess each character by hand •Write a program

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asby Write program

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asby Get solution

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asby Get points

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Jeopardy Style 1. Get challenge 2. Solve it 3. Get points

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Attack-Defense •Reverse engineer •Patch ﬂaws •Exploit others •Don't break it

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⚑ Attack-Defense PPP atmail scorebot Shellphish

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Attack-Defense PPP atmail scorebot Shellphish deposit ⚑

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Shellphish Attack-Defense PPP atmail scorebot steal ⚑

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Shellphish Attack-Defense PPP atmail scorebot redeem ⚑

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Shellphish Attack-Defense PPP atmail scorebot availability okay availability check

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Shellphish Attack-Defense PPP atmail scorebot failed availability ☠ ☠can’t steal

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Attack-Defense DEF CON CTF Finals

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Rubix

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Rubix

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Rubix 54 Rubik's cube instructions …becomes shellcode

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Lab RATs on Rubix Lab RATs posted a write-up: https://blog.rpis.ec/2017/08/defcon- ﬁnals-2017-introduction-rubix.html

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Lab RATs on Rubix 1. write 9-bit to 8-bit netcat 2. analyze 9-bit strings in libc 3. symbolize libc 4. ﬁgure out how main() gets called

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Lab RATs on Rubix Now the actual analysis starts…

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Attack-Defense •How is it supposed to work? •How can we attack it? •How can we defend it?

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Attack-Defense •Get points by capturing ﬂags •Lose points by having ﬂags captured •Lose lots of points by failing checks

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Attack-Defense Complicated, frustrating, fun!

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CTF Extremely ambitious

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CTF •Running Smoothly •Fair Contest •Fun Challenges

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Running Smoothly

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Running Smoothly Starts early

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Running Smoothly Who's on the team?

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Legitimate Business Syndicate •Half 2005-2007 university team •Half 2012 coworkers

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Legitimate Business Syndicate in 2006

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Legitimate Business Syndicate •August 2012: ddtek steps down •December 2012: Gyno starts recruiting •February 2013: Proposal submitted •March 2013: Proposal accepted

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Legitimate Business Syndicate •"Reverse engineers" 3/4 of the group •Diﬀerent specialties •Radio: 2014, badger •Hardware: 2015, the year of single- board computers •Esoteric computing: 2017, cLEMENCy

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Legitimate Business Syndicate 100% dependent on Selir's amazing infrastructure

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Legitimate Business Syndicate I started for the database backed web application

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Team Building People grow and change

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Team Building Roles grow and change

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Team Building •Who do you know? •Who do you trust? •Who do you like?

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Communication “It's good.”

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Communication async (chat) is great weekly meetings are great

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Smooth Operation Support your team

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Smooth Operation CTF software is software

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Smooth Operation Automate testing and deployment

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CTF •Running Smoothly •Fair Contest •Fun Challenges

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Fair Contest

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Fair Contest CTF is computer hacking

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Fair Contest CTF is computer system

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Fair Contest Hack the right thing the wrong way

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Fair Contest Hack the wrong thing

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Fair Contest Fix a thing the "wrong" way

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Fair Contest Restrict players more

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Qualifiers •Services on separate hosts •Multiple hosts in diﬀerent locations •Connections get separate container •xinetd and runc •Limit system calls •seccomp

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Finals More complex game More complex problems

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Finals •Keep the game about reverse engineering •(Not OS administration)

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Finals •2013: unprivileged team account, unprivileged service accounts •2014: understood "Superman defense" better

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Superman Defense •Block opponent IPs •Prevent reading the ﬂag

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Cyber Grand Challenge US Defense Advanced Research Projects Agency (DARPA) project starting in 2014

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Cyber Grand Challenge CTF for autonomous computers

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Cyber Grand challenge Extremely formalized

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Challenge Binaries •"CBs" •32-bit i386 •Special CGCEF executable format •Limited system calls •No retained state

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Proof of Vulnerability •"PoVs" •32-bit i386 CGCEF •Demonstrate a vulnerability: •Register control •Memory disclosure •Run by scoring system

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Offline Evaluation •Team interface gives out binaries •Team interface collects replacement CBs, PoVs •Runs availability checks and PoVs in isolation •Designed for reproducibility and audibility

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Finals •2015: restrict system calls •2016: use CGC game format •2017: everything in limited emulator

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Fair Contest Release scoring information

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Fair Contest Think about accessibility

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CTF •Running Smoothly •Fair Contest •Fun Challenges

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Fun Challenges Break expectations

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dosfun4u •Discover that it's a DOS binary •Debug and patch IDA Pro •Start actual reverse engineering

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badger •MSP-430 on physical hardware •custom CDMA radio network

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Consensus Evaluation •CGC's big attack-defense innovation •Everyone sees everyone else's patched binaries •Explosion in number of binaries that need reversing

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1000 cuts / crackme2000 Push teams into automated analysis Hundreds of binaries

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Consensus Evaluation in 2016 Player asks about losing points Service being attacked, that's why "But we're using the same binariess as the winning team"

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Consensus Evaluation in 2017 Rubix expected shellcode to work in availability checks Defenders would add checks to block "evil" or allow "good" shellcode Attackers would build new shellcode to pass checks "Felt like a multiplayer game against humans"

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CTF •Running Smoothly •Fair Contest •Fun Challenges

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CTF Still more to learn!

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CTf More work ahead of us

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CTF Opportunity to grow for more players

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CTF Best way to learn is to do

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Five years with the best group of people I've ever worked with

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Five years building a contest for the friendliest and smartest community I know

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Thanks for making it amazing!

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vito@legitbs.net @vito_lbs