Optimism fixed two critical vulnerabilities in its test network at least a few weeks after learning of the problems, Offchain Labs, which first discovered the vulnerabilities, said on Friday, adding that the fixed security holes in Optimism's April 25 update to its test network would have allowed malicious actors to manipulate the history of the chain and perform other "subtle attacks. On March 22, Offchain Labs reported two vulnerabilities in its testnet to Optimism.