Solutions to Ethernaut Challenges

Introduction

Ethernaut is a wonderful website based game developed by Openzeppelin and played in Ethereum virtual machine. Each level is a smart contract that needs to be ‘hacked’.
This game provides opportunity to learn more about the never ending knowledge of the EVM based smart contracts & use this knowledge to secure or rescue actual contracts in live enviroment i.e Ethereum mainnet.

In this blog post, I’ll share hints & descriptions of the challenges for which I have posted the solutions on github that you can find here.

Pre-requisite

I have solved these challenges in foundry, a smart contract development framework. You can use also hardhat. Before you start, you will need basic understanding of

1. Solidity language
2. Basics of EVM execution flow
3. Familiarity with web3.js or ethers.js

Challenge Spoilers!

1. Fallback

Description

In this challenge the user is provided with a contract called Fallback.sol. The goal of this challenge is to become the onwer of the contract & drain all the funds (Eth).

Hint

Call the contribute() function by sending it some eth & then call withdraw() method to drain all funds! This challenge requires user to be familiar with the following concepts.

1. Fallback functions & when they are triggered.
2. Ownable & access control functionality.

Check out solution & walkthrough here!

2. Fallout

Description

In this challenge the user is provided with a contract called Fallout. The goal of this challenge is to become the onwer of the contract & drain all the funds (Eth).

Hint

This challenge requires user to be familiar with the following concepts.

1. Fallback functions & when they are triggered.
2. Ownable & access control functionality.
3. Attention to detail!

Check out solution & walkthrough here!

3. Coin Flip

Description

In this challenge the user is provided with a contract called Coinflip.sol. The goal of this challenge is win 10 times consecutively by calling the flip() function of the contract.

Hint

This challenge requires user to be familiar with the following concepts.

1. Pseudo-Randomness in computer systems.

Check out solution & walkthrough here!

4. Telephone

Description

In this challenge the user is provided with a contract called Telephone.sol. The goal of this challenge claim the ownership of the contract.

Hint

This challenge requires user to be familiar with the following concepts.

1. Difference between tx.origin & msg.sender.

Check out solution & walkthrough here!

5. Token

Description

In this challenge the user is provided with a contract called Token.sol. The goal of this challenge is to hack the the token contract.

Check out solution & walkthrough here!

6. Token

Description

In this challenge the user is provided with a contract called Delegate.sol. The goal of this challenge claim the ownership of the contract.

Hint

This challenge requires user to be familiar with the following concepts.

1. Solidity delegtecall function & storage layout.
2. Fallback functions.

Check out solution & walkthrough here!

7. Force

Description

In this challenge the user is provided with a contract called Force.sol. The goal of this challenge to send ether to the contract that has no ability to receive ether.

Hint

This challenge requires user to be familiar with the following concepts.

1. Solidity selfdestruct() function from the docs!

Check out solution & walkthrough here!

8. Vault

Description

In this challenge the user is provided with a contract called Vault.sol. The goal of this challenge to unlock the vault.

Hint

This challenge requires user to be familiar with the following concepts.

1. Storage or slot packing technique while contract creation.

Check out solution & walkthrough here!

9. King

Description

In this challenge the user is provided with a contract called King.sol. The goal of this challenge to become the king in such a way that no one should be able to overpay & become the king.

Hint

This challenge requires user to be familiar with the following concepts.

1. Solidity fallback() funtion.

Check out solution & walkthrough here!

10. Reentrance

Description

In this challenge the user is provided with a contract called Reentrance.sol. The goal of this challenge to drain the contract.

Hint

This challenge requires user to be familiar with the following concepts.

1. Checks-effects-interaction pattern
2. Re-entrancy attacks.

Check out solution & walkthrough here!

11. Elevator

Description

In this challenge the user is provided with a contract called Elevator.sol. The goal of this challenge is to set the variable top to true.

Check out solution & walkthrough here!

12. Privacy

Description

In this challenge the user is provided with a contract called Privacy.sol. The goal of this challenge is to set the variable locked to false.

Hint

This challenge requires user to be familiar with the following concepts.

1. Storage or slot packing technique while contract creation.

Check out solution & walkthrough here!

13. GateKeeperOne

Description

In this challenge the user is provided with a contract called GatekeeperOne.sol. The goal of this challenge is to set the entrant variable to tx.origin.

Hint

This challenge requires user to be familiar with the following concepts.

1. Difference between tx.origin & msg.sender.
2. How gasleft() is used in solidity.
3. How solidity type casting works.

Check out solution & walkthrough here!

14. GateKeeperTwo

Description

In this challenge the user is provided with a contract called GatekeeperTwo.sol. The goal of this challenge is to set the entrant variable to tx.origin.

Hint

This challenge requires user to be familiar with the following concepts.

1. Difference between tx.origin & msg.sender.
2. Properties of XOR operations.
3. Contract creation mechanism & extcodesize() function.

Check out solution & walkthrough here!

15. Naught

Description

In this challenge the user is provided with a contract called Naught.sol. The goal of this challenge is to transfer the tokens before the timelock period.

Hint

This challenge requires user to be familiar with the following concepts.

1. Basic working of ERC20 tokens.
2. Understanding of approve() & transferFrom() functions.

Check out solution & walkthrough here!

16. preservation

Description

In this challenge the user is provided with a contract called Preservation.sol. The goal of this challenge is to claim the ownership of the contract.

Hint

This challenge requires user to be familiar with the following concepts.

1. How delegatecall & storage layout works in solidity smart contract.

Check out solution & walkthrough here!

17. Recovery

Description

In this challenge the user is provided with a contract called Recovery.sol. The goal of this challenge is to claim the ownership of the contract.

Hint

This challenge requires user to be familiar with the following concepts.

1. How a smart contract address is predicted or computed with create() & create2().

Check out solution & walkthrough here!

18. Magic Number

Description

In this challenge the user is provided with a contract called Magicnumber.sol. The goal of this challenge is deploy a contract that returns ‘42’ but only 10 opcodes are allowed no more!.

Hint

This challenge requires user to be familiar with the following concepts.

1. Compiler bytecode & opcodes. For reference visit, https://evm.codes
2. Create2 & Create opcodes for contract creating.
3. Solidity assembly.

Check out solution & walkthrough here!

19. Alien Codex

Description

In this challenge the user is provided with a contract called AlienCodex.sol. The goal of this challenge is to claim the ownership of the contract.

Hint

This challenge requires user to be familiar with the following concepts.

1. Solidity Integer overflow/underflow.
2. Solidity storage layout.

Check out solution & walkthrough here!

20. Denial

Description

In this challenge the user is provided with a contract called Denial.sol. The goal of this challenge is to place a mechnism such that the owner cannot withdraw ether from contract even though it has it.

Hint

This challenge requires user to be familiar with the following concepts.

1. Solidity fallback() funtion.

Check out solution & walkthrough here!

21.

Description

In this challenge the user is provided with a contract called Shop.sol. The goal of this challenge is to set the variable price to be less than 100.

Check out solution & walkthrough here!

22. Dex

Description

In this challenge the user is provided with a contract called Dex.sol. The goal of this challenge is to drain token0.

Check out solution & walkthrough here!

23. DexTwo

Description

In this challenge the user is provided with a contract called DexTwo.sol. The goal of this challenge is to drain token0 & token1 from the dex.

Check out solution & walkthrough here!

Conslusion

That’s all folks. I hope this write-up helped you. See you next time.