Panic on Ethereum: double spend alert... And wild fork!

Friday, August 27 was an eventful day for Ethereum. A bug affecting an old version of its main client software, Geth, caused a separation of the blockchain for more than half of the nodes. There was more fear than harm: the situation returned to normal within hours.

Ethereum and Geth: don’t forget the updates!

The bug affects versions 1.10.7 and earlier ofEthereum‘s main client software, Geth. Surprisingly, at the time of the split (separation of the blockchain into two different versions), 75% of the network nodes were using an outdated version.

Being prior to the Londonhard fork, all nodes must update their client software. It also affects most blockchains using their own version of theEthereum Virtual Machine. To understand how a simple transaction caused a chain split, you should read Kelvin Fichter’s summary.

This fork presented a danger: the possibility of double-spending. By making a transaction on one chain and then replacing it on the other, it was possible to spend your ethers twice. This is the most feared attack on a blockchain network. However, despite the severity of the problem, only one smart guy managed to exploit the flaw on Ethereum. On the Binance Smart Chain, a sharp mind was also able to take advantage of it.

A fork without consequences

When a blockchain is forked, the longest chain always wins. So, fortunately for etherists, the reaction was quick. Despite the fact that more than half of the network nodes were affected, the miners immediately updated their version of Geth. Most of the hashing power was then concentrated on the “valid” chain.

This is Guido Vranken, developer of Telos EVM – a version of the Ethereum Virtual Machine on the Telos blockchain – who discovered the bug first. He informed the Ethereum core developers immediately, and the patch was available by August 24. Moral of the story: update your node!

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