Ethereum’s Pectra Upgrade Faces Setback on Sepolia Testnet

The Ethereum Pectra upgrade encountered unexpected errors on the Sepolia testnet, worsened by an exploit that triggered empty block mining, according to Ethereum developer Marius van der Wijden.

Pectra rolled out on Sepolia at 7:29 AM on March 5, but developers immediately noticed errors on their Geth nodes and an increase in empty blocks.

The issue stemmed from the deposit contract triggering a transfer event instead of a deposit event, causing transaction processing failures.

Edge Case Exploit Causes Further Disruptions

Although a fix was deployed, van der Wijden said the team overlooked an edge case, which an unknown attacker exploited by sending a zero-token transfer to the deposit address, triggering the error again.

“After a few minutes, we saw a lot of empty blocks again, so we looked into the transaction pools and found another offending transaction triggering the same edge cases.”

Initially, developers suspected an honest mistake by a validator, but later discovered that the transaction came from a new account funded by a faucet—confirming the attack.

Developers Quietly Deploy Fix to Avoid Further Exploits

Since Ethereum’s ERC-20 standard allows zero-token transfers, the attacker did not need to own any tokens to interact with the contract.

“The only way to stop the attack was to filter out all transactions interacting with the deposit contract. So we made a private fix and deployed it to key DevOps nodes.”

To prevent the attacker from reacting in real time, the fix was kept private, and only selected nodes were updated to restore normal block production.

By 2 PM, all nodes had been patched, and the attacker’s transaction was successfully mined.

Incident Isolated to Sepolia, But Pectra Upgrade Faces Delays

Van der Wijden confirmed that despite the glitches and attack, Ethereum’s finalization process was never compromised. The issue was isolated to Sepolia due to its use of a token-gated deposit contract, which differs from the mainnet contract.

This isn’t the first testnet issue for Pectra—its Holesky testnet launch on Feb. 26 also faced challenges. As a result, developers have postponed the Pectra upgrade for further testing.

Pectra Follows Dencun Upgrade and Ethereum Foundation Restructuring

Pectra is the next major upgrade following Ethereum’s Dencun hard fork, which rolled out on March 13, 2024 and significantly reduced Layer-2 transaction fees while improving Ethereum rollup economics.

Meanwhile, the Ethereum Foundation recently announced a new leadership structure, appointing Hsiao-Wei Wang and Tomasz Stańczak as co-directors to guide the network’s future development.

With Pectra’s timeline now uncertain, Ethereum’s next upgrade will undergo additional scrutiny to prevent further disruptions before reaching mainnet.