Bitcoin Core v30 Bug Can Delete Files When Migrating Legacy Wallets

Bitcoin Core developers warned users on Monday of a wallet migration bug in versions 30.0 and 30.1 that can delete files and result in fund loss.

The issue occurs under specific conditions and affects migrations from old Bitcoin Core wallets that were never renamed or upgraded.

Lacie Zhang, market analyst at Bitget Wallet, told Cointelegraph that the bug is triggered when the software attempts to migrate an unnamed legacy “wallet.dat” file stored in a custom wallet directory, often defined using “-walletdir” setting, while pruning is enabled.

In these cases, the migration can appear to complete successfully, but the cleanup logic mistakenly deletes the entire wallet directory, and if a user does not have an external backup, “loss of access to funds is effectively guaranteed because all local wallet files are removed.”

Shawn Odonaghue, community lead at layer-3 blockchain Orbs, told Cointelegraph that the bug primarily impacts “very old wallet setups,” and that users with a hardware wallet or modern wallet software are unlikely to experience such issues.

Related: Bitcoin Core wins rare praise as independent audit finds no serious flaws

​Bitcoin Core pulls binaries and prepares fix

Bitcoin Core 30.1 was released on Jan. 1 and the wallet migration bug was publicly disclosed on Monday, with developers pulling the 30.0 and 30.1 binaries from the official download site.

The project told users not to use the wallet‑migration tools until a fixed release, Bitcoin Core 30.2, is available, stressing that existing users who are not attempting migrations can continue running their nodes as normal.

Zhang added that technically proficient users can assess their exposure by checking whether they are running Bitcoin Core v30.0 or v30.1, determining whether their wallet is a legacy wallet, inspecting “debug.log” to see whether pruning is enabled and whether any migration attempts have already occurred, and by reviewing the directory layout to confirm whether “-walletdir” points to a custom or mounted location.

“Risk is highest if all these conditions are present and a migration has either been attempted or is pending,” she said. “If no migration has occurred yet, users should immediately back up the entire data directory to external media and avoid restarting or upgrading until moving to version 30.2 or later.”

Related: Bitcoin devs flocked back to work amid a big year for crypto

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 make up almost 22%. 

That dominance means even a narrowly scoped wallet bug can matter for the wider ecosystem.

“The bigger takeaway is concentration risk,” Odonaghue said. “Bitcoin Core has a massive share of the ecosystem, there aren’t many truly mainstream alternatives… when one implementation becomes the default, any bug or design decision has outsized impact.”

Zhang added that while the bug was not “consensus-critical,” its impact shows how wallet-layer issues can still scale into ecosystem-wide problems when a single implementation dominates usage.