Ethereum Warns of Test Attack on Glamsterdam
On Sepolia, an attacker with free test ETH could disrupt the block auctions. The test is crucial for Glamsterdam, while client teams have until September 29 to deliver software.
Key Takeaways
- Ethereum developers warn that the Glamsterdam test on Sepolia could be disrupted by an attacker with free test ether and fake builders.
- Such an attacker could repeatedly win block auctions and then refuse to release the transactions, undermining the upgrade test.
- Developers have until September 29 to release Sepolia-ready software; the next public test on Hoodi is scheduled for October 27.
Ethereum developers warn that the upcoming Glamsterdam test on Sepolia could be disrupted by an attacker with free test ether and multiple fake builders. According to the developers, someone like that could repeatedly win the block auctions and then refuse to deliver the transactions. That would not affect mainnet funds, but it would affect the test needed to roll out the upgrade properly.
What Could Go Wrong on Sepolia
Glamsterdam shifts the relationship between validators and specialized block builders into the Ethereum protocol itself. Builders put transactions together and bid on them, after which a validator accepts the winning bid. After that, the builder is supposed to release the underlying transactions.
On a free testnet, the developers say that is easy to abuse. A malicious party can place extremely high bids, keep winning, and then withhold the payload. Ethereum consensus developer Potuz said during the core developer call that he could simply set up a thousand builders, rotate them, and keep placing high bids without delivering payloads.
Why Developers Are Extra Alert
The warning came a day after a major private rehearsal finished the transition to Glamsterdam and pushed the block gas limit toward 200 million without losing finality. At the same time, client teams have until September 29 to release Sepolia-ready software. That leaves seven days before the fork, about half of the usual 14 days for security reviews and bug bounty tests.
Developers accepted that shorter window because Sepolia is relatively centralized and easier to recover if something goes wrong. Builder software from Titan and Ultrasound also has not yet gone through a Glamsterdam fork transition, which leaves one more gap before the upgrade can really be called mainnet-ready.
What This Means for Ethereum
The warning shows that Glamsterdam's test phase is not just about speed or capacity, but also about practical security. The Ethereum Foundation has also already warned that some tools may not keep working properly as the network moves toward Glamsterdam, and is urging developers to test software on Platåberget. For European crypto followers, that matters because these testnet issues often decide how smoothly a major upgrade can later go live on mainnet.
The next public test on Hoodi is currently scheduled for October 27. Developers will decide after the Sepolia test whether that date stays in place, while a mainnet activation has not yet been scheduled.
