Exposing An $18 Million USD Smart Contract Vulnerability

Last Winner: Quietly Launched, Inexplicably Popular

Unknown Sources of ETH Funding

Looking At Promotion And Contract Code

DApp Game Airdrop Vulnerabilities

  • Starting a transaction on a contract address with 0.1 Ethereum
  • Many trading statuses are failures
  • Successful transactions invoking many internal transactions
  • Complicated internal transaction call logic, accompanied by the creation and self-destruction of a large number of contracts

AnChain.AI Anomaly Detection

Analyzing Attack Profitability

The Story Behind BAPT-LW20

BAPT-LW20 Steals The Game’s Grand Prize

Who Is Behind BAPT-LW?

The 0x20C9 address was the first to successfully exploit the original Fomo3D airdrop vulnerability and receive rewards.

Why Is Last Winner So Attractive?

Last Winner = Hackers’ ATM!

Who Is next?

Timeline of BAPT-LW20:

  • 2018/07/06 Fomo3D game contract online
  • 2018/07/08 One developer from FOMO3D’s competitor discovers and exploits airdrop vulnerabilities
  • 2018/07/20 Fomo3D game growing very popular in China
  • 2018/07/20 BAPT-LW20 Hacker team activates
  • 2018/07/21 BAPT-LW20 Team Successfully Utilizes Fomo3D Airdrop Vulnerability for the First Time
  • 2018/07/23 BAPT-LW20 Team Attacks copycat game Mouse RatScam
  • 2018/07/23 Péter breaks the Fomo3D airdrop vulnerability in Reddit
  • 2018/07/24 BAPT-LW20 Hacking team attacking FoMoGame
  • 2018/07/26 BAPT-LW20 Hacker team deploys new version of attack contract 0x5483
  • 2018/08/06 Last Winner game goes online
  • 2018/08/07 Last Winner game grows more popular
  • 2018/08/07 BAPT-LW20 Hacker team starts attacking Last Winner
  • 2018/08/09 Ethereum’s unconfirmed transaction volume hit a new high in the year
  • 2018/08/10 BAPT-LW20 The hacker team transfers funds from the old contract and continues the attack with the new version of the contract
  • 2018/08/14 BAPT-LW20 The hacker team deploys a new version of the attack contract and starts attacking a new contract
  • 2018/08/17 BAPT-LW20 Hacking team wins Last Winner Grand Prize Award of 7,754 ETH

Technical Overview

  • The random source used by the airdrop game to control the probability of winning can be obtained in advance
  • Whether the user can get the airdrop reward and the bonus can be calculated in advance in another contract to determine the subsequent manipulation logic.
  • The Fomo3D airdrop mechanism is made to allow only non-contracted addresses (ordinary humans). However, there is a loophole in judging it, and the restriction can be bypassed by participating in the game during the construction of the contract (ie, in the contract construction method).

Attack Variable 1 — Airdrop and Mining

  1. Increased attack success rate
  2. Reduces the number of attack contract deployments and greatly reduces the consumption of gas.

Attack Variable 2 — Probability Of Winning

Attack Variable 3 — Exploiting Bugs In Airdrop Probability Calculations

About AnChain.AI

References

Acknowledgements

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AnChain.AI

AnChain.AI

Blockchain data analytics firm providing security, risk, and compliance solutions.

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