Blockd has put 3 Ether in a very vulnerable smart contract. If you can get past our active security, you win it.

Blockd is back again risking another 3 Ether to demonstrate Blockd Build.For this demonstration, we’ve created a very vulnerable Ethereum contract. Anybody is able to change the owner of the contract, users are able to withdraw as much Ether as they want, and the Oraclize callback function can be called by anyone. Blockd Build, however, will stop any hacks from occurring despite the contract having these “unknown” vulnerabilities.Anyone can attempt to “hack” the contract below. Blockd will let your transaction through if it’s legitimate, such as a deposit of 1 wei then withdrawal of 1 wei (or even a withdrawal of 0 wei). If the transaction is illegitimate, such as a > 0 withdrawal with no deposit, Blockd will race your transaction to blacklist you before it is executed.The Etherscan link is: https://ift.tt/3cMri7c Build provides custom smart contract security that actively monitors for and intervenes in pending hacks. It traces pending transactions to determine their effect, then blocks the transaction or pauses the contract if malicious actions are going to take place, such as the owner variable being changed by a non-owner, the contract losing more Ether than the sender’s balance, or the Oraclize callback not matching the called API. This strategy means that we do not need to know how a hack was executed to know that we need to block it.We’re using a blacklist to block hacks as a public example so that many people can test the security. On real contracts, a pause (such as tBtc’s recent temporary pause)--using a pre-signed transaction by the contract's owner so that Blockd needs no special privileges--that stops all hack attempts and gives developers time to address the problem is a more likely blocker alternative, although every system has different needs.Blockd Build is in no way meant to replace audits and bug bounties, but to complement them with another layer of security in case any bugs slip through the cracks.For information on how the system works or to contact us, you can visit blockd.co.P.S. We’ll be withdrawing the Ether and shutting down the security after a day or so or if we start running low on gas funds needed to block the hacks.

Submitted May 21, 2020 at 07:23PM