Bitcoin Core v30 bug risks fund loss in legacy wallet upgrades
News
Bitcoin Core developers on Monday cautioned users about a wallet migration bug in versions 30.0 and 30.1 that can delete local files and potentially lead to loss of funds. The flaw occurs under specific circumstances involving migrations from older Bitcoin Core wallets that were never renamed or upgraded.
Lacie Zhang, a market analyst at Bitget Wallet, said the issue is triggered when the software attempts to migrate an unnamed legacy “wallet.dat” stored in a custom wallet directory, typically set via the “-walletdir” option, while pruning is enabled.
In these cases, the migration may appear to finish successfully, but a cleanup routine can mistakenly remove the entire wallet directory. If no external backup exists, access to funds can be lost because all local wallet files are deleted.
Shawn Odonaghue, community lead at layer-3 blockchain Orbs, said the problem primarily affects very old wallet configurations. Users with hardware wallets or contemporary wallet software are unlikely to encounter the issue.
Bitcoin Core pulls binaries and prepares fix
Bitcoin Core 30.1 was released on Jan. 1, and the migration bug was publicly disclosed on Monday. Developers have removed the 30.0 and 30.1 binaries from the official download page.
Bitcoin Core 30.0 and 30.1 Bug | Source: Bitcoin Core Project
The project advised users not to use wallet‑migration tools until a fixed release, Bitcoin Core 30.2, becomes available. Existing users who are not attempting migrations can continue running their nodes as normal.
Zhang said technically proficient users can assess their exposure by confirming they are on Bitcoin Core v30.0 or v30.1, determining whether their wallet is a legacy wallet, reviewing “debug.log” to see if pruning is enabled and whether any migration attempts have occurred, and checking the directory structure to verify whether “-walletdir” points to a custom or mounted location.
She added that risk is highest if all these conditions are present and a migration has been attempted or is pending. If no migration has occurred yet, users should back up the entire data directory to external media immediately and avoid restarting or upgrading until moving to version 30.2 or later.
Bitcoin Core dominates nodes
According to Bitcoin data tracker Coin Dance, Bitcoin Core currently accounts for about 78% of reachable Bitcoin nodes, while other implementations such as Bitcoin Knots represent almost 22%.
Bitcoin Core runs most nodes | Source: Coindance
That concentration means even a narrowly scoped wallet bug can have broader implications. Odonaghue noted the concentration risk, saying that with Bitcoin Core holding a large share of the ecosystem and few mainstream alternatives, any bug or design choice can have an outsized impact.
Zhang said that while the flaw is not consensus‑critical, it demonstrates how wallet‑layer problems can scale across the ecosystem when a single implementation dominates usage.
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