Wallet Migration Failure May Delete Unrelated Wallet Files In Bitcoin Core 30.0 and 30.1

[Ava Chow]

Hi all,

We have become aware of a wallet migration bug introduced in Bitcoin
Core 30.0 and 30.1. Under rare circumstances, when the migration of a
wallet.dat file fails, all files in the wallet directory may be deleted
in the process, potentially resulting in a loss of funds. A fix is
forthcoming and will be released as 30.2, but out of an abundance of
caution we have removed the binaries for affected releases from
bitcoincore.org.

At this time, we ask users to not attempt wallet migrations using the
GUI or RPC until v30.2 is released. All other users, including existing
wallet users, are unaffected and can keep using existing installations.

Specifically, it requires the presence of a default (unnamed) wallet.dat
file, which has not been created by default since 0.21 (released 5 years
ago), that fails to be migrated or loaded. One condition that may
trigger this is when pruning is enabled, and the wallet was unloaded
while pruning happened.