A transaction processed in Ethereum block 11,234,873 on November 11, 2020 exposed a consensus difference between older and updated versions of the Geth client, separating some nodes from the canonical chain and disrupting infrastructure used by wallets, exchanges and applications.
The event was not a scheduled Ethereum protocol upgrade. Updated Geth versions and other Ethereum clients continued following the longer chain, while vulnerable older Geth installations rejected the block because they calculated a different result. Infura, which operated affected Geth versions in parts of its infrastructure, suffered what it called its most severe service interruption in four years.
That distinction matters. Ethereum did not cease producing blocks across the entire network, and the incident did not create a lasting new cryptocurrency. It nevertheless demonstrated that client-version differences and concentrated dependence on one remote-procedure-call provider could make a functioning blockchain inaccessible to many users.
A dormant bug became a consensus break
Geth is software used to validate Ethereum blocks and expose network data to applications. According to Geth team lead Péter Szilágyi’s same-day technical account, version 1.9.7 had introduced an incorrect shallow-copy behavior affecting implementation of EIP-211. The bug remained dormant until it was reported through Ethereum’s vulnerability process on July 15, 2020.
Developers corrected the behavior in Geth 1.9.17, released on July 20, without publicly identifying it as a consensus-critical security fix. Publicizing an exploitable vulnerability before operators upgraded could itself have invited an attack. The resulting tradeoff was that operators running version 1.9.16 or earlier did not know that remaining on those releases could eventually separate them from upgraded nodes.
On November 11, a transaction in block 11,234,873 exercised the affected behavior. Updated clients calculated one state result; older Geth clients calculated another and rejected the block. A Geth repository issue opened that day preserves an operator’s invalid-Merkle-root error at the exact block, providing a contemporaneous technical record independent of later summaries.
Calling the episode an “unannounced hard fork” captured the incompatibility but could also mislead. Developers had not adopted new community-approved consensus rules. The updated client restored behavior intended by the existing specification, while the older software retained the faulty implementation. Operationally, however, the two groups could not agree on the same block, producing the effect of a partial chain split.
Infrastructure dependence amplified the failure
Infura reported its Ethereum Mainnet API outage at 08:12 UTC. Its archive-data, filter, log, WebSocket and HTTPS interfaces were among the affected components. At 11:23 UTC, Infura attributed the failure to infrastructure locked to older Geth releases, including versions 1.9.9 and 1.9.13, and said components running version 1.9.19 or later were unaffected.
The interruption propagated beyond Infura’s own status page. Contemporaneous reporting documented problems for MetaMask, which used Infura as a default provider, and temporary ether and ERC-20 withdrawal suspensions at Binance and Bithumb. Binance resumed withdrawals at approximately 10:00 UTC. Those actions were operational precautions by individual services, not evidence that Ethereum had globally disabled transfers.
BlockCypher later documented that its own older Geth dependency stalled at the same block. Its nodes detected the problem at 07:08 UTC, identified the Merkle-root mismatch and deployed a newer Geth version during its recovery. The separate provider record confirms that the problem was not unique to Infura.
What November 11 established
The incident exposed two related risks: implementation diversity only helps when infrastructure operators actually use and cross-check different clients, and a decentralized ledger can still be reached through centralized service bottlenecks. Applications relying on one provider inherited that provider’s client-version and recovery decisions.
No ether price, return or trading-volume claim is made here. The protocol and outage records do not establish a standardized market window or demonstrate that the split caused a particular price movement.
Later clarification
An Ethereum Foundation security disclosure published after November 11 identified the vulnerable range as Geth 1.9.7 through 1.9.16 and said roughly 30 blocks were produced on the minority side before affected nodes returned to the canonical chain. That later clarification supports the technical reconstruction but is not treated as information available at the incident’s outset.
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