Two Vulnerabilities Caught in Optimism Testnet

Developers caught two vulnerabilities in the testnet of Optimism, the second-largest Ethereum Layer 2 by assets.

Members of Offchain Labs, the company building Ethereum Layer 2 Arbitrum, today said they found the bugs in Optimism’s fraud proofs during a testnet implementation.

“We found several critical attacks that compromise the safety and liveness of Optimism’s proposed dispute system,” wrote Raul Jordan, distributed systems engineer for Offchain Labs. “The attacks make it easy for an evil party to get a fraudulent claim accepted on chain, or defeat the honest party.”

The Optimism team said on X after Offchain Labs disclosed their findings, that they are “happy to report” that no critical vulnerabilities that would be able to bypass the safety mechanisms were reported during an audit with blockchain security firm Sherlock.

They did however send a special thank you to the Offchain Labs team for reporting the two vulnerabilities prior to the start of the Sherlock audit contest.

Optimism did not immediately reply to a request for comment from The Defiant.

In one of the attack vectors, the attacker can wait until the last second, make a move, and win a dispute, Jordan explained on X today. The last attack is resource exhaustion, making it very difficult for the honest parties to successfully defend, although it was already publicly known.

Optimism’s native OP token dropped 4.8% on the news today. OP has had a dismal month, shedding nearly 40% of its price, changing hands currently for $2.32, while Ethereum lost 10% in the same period.

The network shows a $2.4 billion market capitalization and $879 million in total value locked (TVL) according to DefiLlama.

Still, Optimism has been teeming with activity in recent months. On April 18, the team offered $22 million in grants to Superchain efforts, a Optimism-based tech stack; the day after Worldcoin launched an Optimism-powered Layer-2 blockchain; the network airdropped $40 million to artists and creators on Feb. 22, and on Feb. 13 it set in motion a security council as part of a move towards progressive decentralization.

A blog post by the Offchain Labs team explains that they disclosed the two “serious vulnerabilities” to the OP Labs team, who asked for the information to remain out of the public’s eye until properly addressed.

According to Ed Felten, co-founder of Offchain Labs, the vulnerabilities allowed a malicious party to force the OP Stack fraud proof mechanism to accept a fraudulent chain history, or to prevent the OP Stack fraud proof mechanism from accepting a correct chain history.

The problems stemmed from flaws in how the OP fraud proof design handles timers.

Felten, who wrote the blog post, added that fraud proof protocols and their timing aspects are very difficult to design; the latter considered one of the most subtle aspects of the design process.

“We coordinated closely with the OP Labs team on this disclosure,” posted the Offchain Labs X account on April 26. “We’re all on team Ethereum, and happy to lend resources to make Ethereum safer for everyone.”