Ethereum: 'Any teenager' can derail the Glamsterdam test

Winning a bid, then delivering nothing. This is the scenario that worries Ethereum developers ahead of the Glamsterdam test on Sepolia, scheduled for October 6. On this test network, the ether used for bidding has no market value. A malicious actor could therefore repeatedly win block construction and then withhold the transactions they promised to place there. The risk concerns the tests on Sepolia, not the funds deposited on the main network.

Key Points

• Glamsterdam integrates the builder market into the protocol via ePBS (EIP-7732), with unconditional payment to the proposer.
• On a testnet, free ether makes payload retention costless: empty slots and an unusable chain.
• Proposed countermeasures are limited to whitelists of builders and a minimal deposit to bid.
• Client teams have half the usual time for cross-review before Sepolia.

Glamsterdam: Why a builder could block transactions

On Ethereum, specialized actors, called builders, gather the transactions intended to form a block. A validator then chooses a proposal. With Glamsterdam, this relationship must be directly embedded in the network rules: builders bid to provide the block content, and then the winner must publish it.

The mechanism provides a financial counterpart. According to Ethereum's technical proposal, the validator receives payment even if the winning builder does not deliver the transactions. On the main network, withholding promised content can therefore cost ethers with real value.

On Sepolia, the same payment is made in test ether. During the developers' call on September 17, the developer known by the pseudonym Potuz described an attacker capable of creating numerous builder identities, systematically outbidding, and never publishing the transactions. If this strategy were repeated, it could leave blocks empty and hinder teams using Sepolia to test their applications.

Developers are thus discussing protections to revert to locally constructed blocks and exclude builders who do not deliver. They must also prevent an excluded actor from immediately returning under another identity. No definitive solution was announced during the call. Each new update of the Ethereum network is an event in the cryptosphere -- Source: X JDC Account

Sepolia: Seven days of verification before the public test

The other topic of discussion concerns the timeline. Teams developing Ethereum software have been asked to release a version compatible with Sepolia by September 29 at the latest, if possible earlier. This would leave seven days before the test on October 6. The usual procedure allows for at least fourteen days between the availability of this software and its deployment on a first test network.

This timeframe is particularly for security checks and bug hunting. One developer reported that halving it would limit the time available for these verifications. Participants nonetheless maintained the planned date for Sepolia: this network has a limited number of validators and would be easier to restore if the test goes wrong.

Sepolia is not the final examination before Ethereum. Another test on Hoodi is tentatively planned for October 27, depending on the results of the first. No date has yet been set for the activation of Glamsterdam on the main network.

The upcoming tests will therefore need to answer two concrete questions: do the new blocks function as expected, and do the protections prevent a builder from permanently disrupting a network where bidding costs them almost nothing? More than a few weeks before launching the machine...

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