Bitcoin Core Discloses High-Severity Bug That Could Halt Mining

Bitcoin Core has disclosed a high-severity vulnerability, tracked as CVE-2025-62861, that could leave a mining node unable to build block templates after a chain reorganization, halting block production on that node until an operator manually restarts it.

The flaw affected five releases: versions 28.0, 28.1 and 28.2 in the 28.x series, and versions 29.0 and 29.1 in the 29.x series. Bitcoin Core fixed the bug in October 2025, including in version 30.0. The affected releases have since reached end of life and no longer receive support, which means any operator still running them carries the exposure without a patched upgrade path inside those branches.

Security researcher Niklas Goegge responsibly disclosed the issue. The disclosure followed the project's standard practice of publishing details only after patched releases had time to propagate — though Bitcoin Core did not state how many nodes ran vulnerable versions at the time of disclosure, a gap that limits any assessment of real-world exposure.

What does the flaw actually do?

The bug sits in Bitcoin Core's handling of TRUC transactions, also known as version 3 transactions — a transaction type designed to make fee management and mempool policy more predictable.

The failure sequence unfolds in three steps:

• A chain reorganization replays transactions into the mempool.
• Bitcoin Core fails to block the TRUC sibling-eviction mechanism during that replay, leaving the mempool in an inconsistent state.
• That inconsistency causes block-template validation to fail, so the node cannot produce a candidate block for a miner.

A block template is the candidate block the software assembles for a miner to extend the chain. Without a valid template, an affected mining node stops contributing block production entirely; only a restart clears the inconsistent mempool state and resumes operations.

In practical terms, a solo miner or pool node running a vulnerable release would go dark after a reorganization of sufficient depth — an operational outage, not a loss of funds. The bug does not put coins at risk directly, but it degrades network reliability precisely when the chain is under stress, since reorganizations themselves are the trigger.

How serious was the exposure?

The severity rating is high, but the practical risk was bounded by two factors. First, the trigger requires a chain reorganization that replays the right class of transactions — an event, not a certainty. Second, the failure is recoverable: a restart restores block production, and other nodes on the network continue building blocks unaffected.

The systemic risk would materialize only if a large share of hash power ran vulnerable releases simultaneously and a widespread reorganization knocked those nodes offline together. Bitcoin Core has not published data on version distribution among miners, so that scenario remains unquantified — a caveat worth attaching to any claim that the network was never in danger.

What happens next?

The remediation is already complete in code: the fix shipped in October 2025 and in version 30.0. The remaining action sits with operators. Any miner or infrastructure provider still on 28.x or 29.x releases must migrate to a supported version, because end-of-life status means no further security patches will reach those branches.

The disclosure also feeds a broader debate over Bitcoin Core's release cadence and its end-of-life policy, which retires branches roughly as new major versions arrive — a pace some operators struggle to match.