An attack on the Ethereum blockchain early Tuesday morning temporarily diverted a small percentage of the network’s nodes to a non-canonical chain.
Ethereum’s mainnet is now operating normally, and the attack is unlikely to be replicated at a larger scale, according to an expert.
The attack was first flagged by Alex S. of Flexpool on the Ethereum R&D Discord shortly after 3 a.m. Eastern time. “Anything wrong with the mainnet again?” he wrote, referring to a chain split that occurred on the network in late August.
Read more: Ethereum Faces Chain Split as Node Operators Fail to Update Geth Hotfix
He noted that some of his nodes were recording the “highest block” of the chain at a block number that technically did not exist, as it was set at a sum greater than the “current block.”
Researchers speculated in Discord that the cause was a peer publishing a version of the chain with invalid proof-of-work.
Ethereum researcher and Go Ethereum software client developer Marius Van Der Wijden told CoinDesk the attack was “experimental” in nature.
“Someone published an invalid chain that was rejected by most clients. ~25% of Nethermind clients accepted the invalid chain,” Van Der Wijden wrote. “Judging from ethernodes, ~20 nodes were affected or 0.8% of the network. I don’t think it was a directed attack against nethermind, but rather someone experimenting and validating their experiment on the live network.”
Tomasz Stańczak, founder of Ethereum infrastructure company Nethermind, posted on Twitter that a public statement would be forthcoming.
Van Der Wijden noted that due to the nature of the attack, it is unlikely that a similar exploit could scale to a degree to have a major impact on the network. Ethereum is validating blocks normally.
Van Der Wijden also noted that a diversity of clients is key for the health of the network, particularly as it prepares for a transition to a new proof-of-stake consensus model.
“Especially with the switch to proof-of-stake, client diversity is extremely important as a well-balanced distribution of clients greatly decreases the probability of creating an invalid chain,” he said.