The Layer 2 network Optimism has repaired two critical vulnerabilities on its testnet at least several weeks after learning of them. 

Offchain Labs, which first identified the vulnerabilities, stated on Friday that Optimism updated its testnet on April 25. The since-fixed security flaws allowed bad actors to manipulate the chain's history and execute other “subtle attacks,” the software firm said.

On March 22, Offchain Labs alerted Optimism about two issues with its testnet: Bad actors could force the OP Stack fraud-proof mechanism to accept a fraudulent chain history, and an exploiter could prevent it from accepting a correct chain history.

“These are difficult problems to solve,” Offchain Labs, which is a competitor of Optimism, said in the statement. It added that fraud-proof …