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Bitcoin miners use specialized computers to race to add the next valid block. Adding blocks and validating transactions is how they earn rewards.

This week, Bitcoin Core developers flagged a “high severity” software flaw in a November 10 report. The flaw could stop affected mining nodes from preparing new blocks.

Explained: What is Bitcoin mining? (6:23)

This could potentially cost miners opportunities to earn rewards.

As per the report, the flaw was reported to developers in September 2025 and patched that October, over a year before its public disclosure. Developers waited until the last vulnerable software version reached end of life on Oct. 27, 2026, before releasing any further details.

The flaw did not directly expose Bitcoin holdings to theft. 

Miners’ reliance on Bitcoin Core

Bitcoin Core is the open-source software descended from the original Bitcoin code released by Satoshi Nakamoto in 2009.

The software enables nodes to verify transactions and maintain the network with the addition of newer blocks. 

For miners, the software also prepares transactions that mining machines compete to add to the blockchain.

Before mining a new block, a computer gathers pending transactions into a draft block. The mining machines then compete to produce a valid block, with the successful miner earning 3.125 BTC in newly issued Bitcoin, plus transaction fees. 

If the software, however, fails to curate that template, the machines are essentially left with no valid work to perform or blocks to add.

What went wrong with Bitcoin Core

Bitcoin Core has identified the vulnerability as CVE-2025-62861. It has been found to have stemmed from how Bitcoin Core handled transactions after a blockchain reorganization.

In a reorganization situation, the network replaces recently accepted blocks with a competing chain. Transactions from the discarded blocks are normally returned to the pool of unconfirmed transactions, known as the mempool.

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Under specific conditions, the bug could remove a transaction while leaving others that depended on it. This left the software with an inconsistent transaction list and prevented it from producing valid block templates.

  • Security researcher Niklas Goegge reported the vulnerability on Sept. 26, 2025, and developer Greg Sanders submitted a fix

  • Bitcoin Core 30.0 shipped the patch on Oct. 10, 2025, followed by versions 29.2 on Oct. 14 and 28.3 on Oct. 17

  • The flaw affected versions 28.0 through 28.2 and 29.0 through 29.1

What the bug could have cost Bitcoin miners

The immediate consequence for affected miners would be lost mining time.

Restarting the node would first rebuild its pending transaction list and temporarily restore normal operations. However, the problem could return if another qualifying reorganization occurred.

Upgrading to a patched version was needed to remove the underlying vulnerability. Bitcoin Core’s disclosure did not report exploitation or financial losses. 

The vulnerability majorly unleashes a threat of disrupted mining operations and missed rewards for the miners, and not a threat of BTC getting stolen.

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