Attacker Stymies Ethereum’s Pectra Upgrade on Sepolia Testnet

Ethereum’s highly anticipated Pectra network upgrade on the Sepolia test network did not go as planned, due to an attacker repeatedly sending zero-value transfers.

On Mar. 5, Ethereum developers rolled out the Pectra upgrade on Sepolia as scheduled. Although the network could finalize transactions, the Ethereum Foundation’s Tim Beiko said in an X post that an issue in the network’s custom deposit contract had caused nodes to produce empty blocks. In a follow-up X post, Beiko said developers had identified and deployed a fix.

Speaking about the incident in a Mar. 8 blog post, Ethereum developer Marius Van Der Wijden said nodes continued producing empty blocks even after they had deployed the fix. Upon further inspection, they discovered that someone had been sending zero-token transfer transactions, triggering the empty blocks

“First, we thought that someone from the trusted validators had made a mistake, but we quickly realized that this transaction originated from a new account recently funded by the faucet,” Wijden said.

“The ERC20 standard does not forbid 0 token transfer, this allows anyone (even if they don’t own any token) to transfer 0 tokens to another address which will emit an event. The “attacker” realized this edge case that we missed and sent a transaction that triggered the behavior again.”

Wijden said they had to filter out all transactions that interact with the deposit contract to stop the attack. Once they did, the nodes started producing full blocks again, ending the issue.

The Sepolia incident isn’t the first time Ethereum developers have encountered a problem with the Pectra upgrade on a testnet. During the Holesky launch, the network ran into finalization issues due to a bug in the code.

Following the issues with the Pectra launch on Sepholia and Holesky, Ethereum developers agreed during the Ethereum All Core Developers (ACD) call on Mar. 6 to launch a “shadow fork” to continue tests and research ahead of the mainnet launch.

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