'How to Solve the Ethernaut Game's Level 5: Token' by Kamil41492605 solidity smartcontractssolidity
// SPDX-License-Identifier: MIT pragma solidity ^0.6.0; contract Token { mapping balances; uint public totalSupply; constructor public { balances[msg.sender]=totalSupply=_initialSupply; } function transfer public returns { require; balances[msg.sender] -=_value; balances[_to] +=_value; return true; } function balanceOf public view returns { return balances[_owner]; } }
To hack this contract first you need to understand the concept of integer underflow and overflow. The overflow is a situation when uint reaches its byte size. Then the next element added will return the first variable element.Let me explain with an example. Note: The hardhat console library is necessary to log to the console in Remix.
If you run this code in Remix, be sure to use compiler version 0.6. As you can see we have a variable named decrease with value a 0. If we subtract 1 from that variable we end up with 255.
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