Optimism loses 20M tokens after L1 and L2 confusion exploited

cointelegraph.com:

The honeymoon period for the Optimism layer-2 scaling solution has been cut short as an exploit in its market maker’s smart contract led to the loss of 20 million OP tokens.

The exploit took place May 26 but has only just been reported to the community. One million tokens valued at about $1.3 million were sold on June 5. An additional one million tokens valued at about $730,000 were transferred to Vitalik Buterin's Ethereum address on Optimism earlier today at 12:26am UTC. The remaining tokens are dormant for now but could be sold at any time or used to sway governance decisions.

Hey folks--in the interest of transparency, we'd like to share some details about an ongoing situation:https://t.co/915vIgRIJGSummary below

OP tokens are the native token for the Optimism Layer-2 (L2) and a portion of the supply was airdropped to network users on June 1. L2 solutions help alleviate congestion on a layer-1 blockchain such as Ethereum.

A summary of events from the Optimism team on Thursday detailed how the 20 million OP tokens were intended to be used by the Wintermute crypto market making firm. After sending two test transactions, the Optimism team sent the full amount of tokens.

However Wintermute discovered that it could not access the tokens because the smart contract it used to accept the tokens was still on L1 and had not been updated to be deployed on Optimism. This technical oversight opened the contract to an attack in which a bad actor took control of the contract on the L2 themselves.

As soon as Wintermute became aware of the problem, it “began a recovery operation with the goal to deploy the L1 multisig contract to the same address on L2,” but its attempt to remedy the situation was too late.

A multisig contract requires