Ethereum developers have warned of a potential attack on the Sepolia testnet during preparations for the upcoming Glamsterdam upgrade. An attacker could use free testnet ETH to manipulate block bids and disrupt block production.

The issue would not directly threaten Ethereum mainnet funds, but it could interfere with testing and delay the evaluation of Glamsterdam-related infrastructure. Sepolia testing is scheduled to begin on October 6, followed by testing on Hoodi on October 27. The mainnet launch date has not yet been finalized.