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I found an example of underflow bug at: Catching Vulnerable Smart Contracts Once and for All

contract UnderflowAttack {
 ...
 function withdraw (uint amount) public {
   require(balances[msg.sender] - amount > 0);
   msg.sender.transfer(amount);
   balances[msg.sender] -= amount; //Underflow
 }
 ...
}

I feel the above contract also exhibits signedness bug. Can somebody please provide me a more specific example of a signedness bug in smart contract?

  • If an underflow happens at balances[msg.sender] -= amount, that same underflow also happens at require(balances[msg.sender] - amount > 0) because the exact same subtraction is being performed. – Jesse Busman Jun 12 at 20:58

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