Ethereum developers delay Hoodi Glamsterdam fork over gas security risks

ChainSecurity said on Thursday that Ethereum developers had postponed the Glamsterdam hard fork on the Hoodi test network because of security problems the auditor identified. The upgrade was scheduled for Monday. ChainSecurity said 13 real-world examples had been identified and responsible disclosure was underway with affected projects. Developers have not set a replacement date for the Hoodi fork.

Ethereum researcher Christine Kim advised node operators to revert to an earlier software release that does not schedule the upgrade. Kim said node operators could alternatively await a new version from the relevant execution client team that cancels the upgrade. Preston Van Loon, a developer on the Prysm consensus client, said a Prysm release removing the scheduled Hoodi upgrade would arrive the same day.

Gas represents the fee for computational work on Ethereum. Glamsterdam modifies charges for creating and accessing stored data through proposals EIP-8037 and EIP-8038. The upgrade also creates a separate gas pool for adding new state.

ChainSecurity's analysis found that the changes undermine assumptions many smart contracts make when external calls fail. Some contracts check gas availability or depend on an out-of-gas failure to defend against insufficient gas griefing. That tactic involves an attacker deliberately providing too little gas, causing a valid operation to fail and become permanently recorded as unsuccessful. ChainSecurity said Glamsterdam could allow some contracts to permanently register failures that the contracts were designed to keep retryable.

ChainSecurity found that Glamsterdam allows gas to be replenished or returned to a contract following a failed call. ChainSecurity also found that repricing can alter the gas required by a call. ChainSecurity said a failure path that previously reverted could now finish even when the contract code remains unchanged. ChainSecurity urged projects to inspect contracts and said the Ethereum Foundation was assessing how many contracts were affected.

Sepolia, another Ethereum test network, activated Glamsterdam on October 6. Sepolia then began producing blocks with a gas limit approaching 200 million, more than three times mainnet's 60 million. Glamsterdam also introduces block-level access lists that allow computers to verify transactions in parallel. The upgrade incorporates the auction determining who assembles each block into Ethereum's protocol rules.

Developers had targeted a mainnet launch for Glamsterdam by the end of 2026. Glamsterdam would precede Hegota, the following upgrade, which is expected in 2027 and could introduce native privacy features.