PSA: Wallet Migration bug present in Bitcoin Core wallet 30.0 & 30.1

[TryNinja]

I just saw this X post from the Bitcoin Core account and thought it was a good idea to share it here for more eyes. I definitely don't want to see anything losing their wallet files for hundreds of Bitcoins.

NOTICE: Wallet Migration bug present in Bitcoin Core wallet 30.0 & 30.1.

Under rare circumstances, migrating a legacy (BDB) wallet can delete all wallet files on the same node. If those wallets aren’t backed up, this can result in a loss of funds.

A fix will become available in Bitcoin Core 30.2. Until that is released, do not migrate legacy wallets using 30.0 or 30.1.

Only the legacy wallet migration process is affected. All other uses are unaffected. You can continue using Bitcoin Core normally, including existing wallets and running a node without wallets.

[MusaMohamed]

If those wallets aren’t backed up, this can result in a loss of funds.

It can be a bug, a severe one and hopefully nobody lost their bitcoins with this bug. Thank you for sharing it here as a reminder and discussion if possible in Bitcoin forum.

This security issue is an indirect reminder on vital importance of wallet backups. Bitcoin with private keys gives us great opportunity to have our own banks but we must secure our own banks by ourselves. Firstly and most importantly, we must do wallet back up, and test our wallet backups before doing anything next like funding our wallets with bitcoins.

[ABCbits]

Bitcoin Core isn't exactly beginner friendly and use fair amount of resource, so i expect people who use it bother to make one or more wallet backup.

For those who can't see the X post) (usually because not logged in), you also can visit https://bitcoincore.org/en/2026/01/05/wallet-migration-bug/.

[Yamane_Keto]

unnamed legacy wallet ("default" wallet) are the only affected wallets. affected number may be very limited.
Fix: https://github.com/bitcoin/bitcoin/pull/34156

It can be a bug, a severe one and hopefully nobody lost their bitcoins with this bug. Thank you for sharing it here as a reminder and discussion if possible in Bitcoin forum.

https://github.com/bitcoin/bitcoin/issues/34128 reported this issue, but did not mention whether had more backups or not.

Bitcoin Core isn't exactly beginner friendly and use fair amount of resource, so i expect people who use it bother to make one or more wallet backup.

it could be an unlucky user who found the wallet file and doesn't know much about Bitcoin.

[OgNasty]

Bitcoin Core isn't exactly beginner friendly and use fair amount of resource, so i expect people who use it bother to make one or more wallet backup.

For those who can't see the X post) (usually because not logged in), you also can visit https://bitcoincore.org/en/2026/01/05/wallet-migration-bug/.

I would expect the same, but you never know.  I'm sure somebody will screw the pooch as they say.  Hopefully not.

I can't remember a more hated release of Bitcoin Core software.  I'm surprised people aren't using this bug to make more noise about it, but maybe it is still early.

[BlackHatCoiner]

The bug went unnoticed, because versions prior 30.0 had an issue with copying the legacy wallet backup. This incident resulted in a ton of Knotz butthurts on X to create just another drama on Bitcoin Core devs.

I was just wondering if any bitcoin was accidentally lost by trying to migrate old wallets, or the developer who reported it just randomly figured it out by testing.

[goldkingcoiner]

I was just wondering if any bitcoin was accidentally lost by trying to migrate old wallets, or the developer who reported it just randomly figured it out by testing.

Hopefully the second one, but statistically I think the first one might be more probable.

The fact that I have not had seen any complaints does kind of make it seem nobody lost enough to ragepost yet. So most likely no massive damage has been done. Nobody has lost millions or even thousands (maybe).

[Donneski]

Wallet migration is one of those things people usually do without expecting any issues so a bug like this can be really costly if someone isn’t careful with backups. It’s good to know the issue is limited to legacy wallet migration but honestly, waiting for 30.2 feels like the safest option for now.

[promise444c5]

https://bitcoincore.org/en/2026/01/05/wallet-migration-bug/

[joker_josue]

I can't remember a more hated release of Bitcoin Core software.  I'm surprised people aren't using this bug to make more noise about it, but maybe it is still early.

This happens to those who have backup files made in older versions, more than 5 years old. Perhaps most people who migrated to v30 had v29 and made their backups from there. So, very few people encountered the problem.

In turn, whoever happened to open an older backup already had a backup of the file safely stored. So, even with the problem, they didn't suffer any losses.

[Yamane_Keto]

Hopefully the second one, but statistically I think the first one might be more probable.

The fact that I have not had seen any complaints does kind of make it seem nobody lost enough to ragepost yet. So most likely no massive damage has been done. Nobody has lost millions or even thousands (maybe).

To lose access to your wallet, it must be a legacy wallet, its name have not been changed (i.e., the "default" wallet), the migration have been completed successfully, and not have any other copies. This is extremely rare.

[vapourminer]

I can't remember a more hated release of Bitcoin Core software.  I'm surprised people aren't using this bug to make more noise about it, but maybe it is still early.

This happens to those who have backup files made in older versions, more than 5 years old. Perhaps most people who migrated to v30 had v29 and made their backups from there. So, very few people encountered the problem.

not being able to drop some older versions wallet.dat backup into my node is main reason i will not run 30.x (im on 29.2 ).

this didnt hit me but i honestly can see me triggering it at some point.

sure everyone rolls with backups but yikes.

[MusaMohamed]

This happens to those who have backup files made in older versions, more than 5 years old. Perhaps most people who migrated to v30 had v29 and made their backups from there. So, very few people encountered the problem.

In turn, whoever happened to open an older backup already had a backup of the file safely stored. So, even with the problem, they didn't suffer any losses.

People who don't make their Bitcoin wallet backups always have risk of losing their bitcoins. This wallet-migration bug is like another warning for such people, even they did not lose bitcoins this time, they must change their practice.
Additionally, forum admin pinned this bug in the News as "Due to a wallet-migration bug, you should not upgrade Bitcoin Core. But if you already did, there's no need to downgrade."

I am not sure when he did it but perhaps after this topic created. This topic is helpful and possibly helped forum admins awared about the bug, and took action with pinning the news; or forum admins knew about this bug somewhere else but generally TryNinja made a very helpful topic with good contribution for Bitcoin users in this forum community.

[cr1776]

Hopefully the second one, but statistically I think the first one might be more probable.

The fact that I have not had seen any complaints does kind of make it seem nobody lost enough to ragepost yet. So most likely no massive damage has been done. Nobody has lost millions or even thousands (maybe).

To lose access to your wallet, it must be a legacy wallet, its name have not been changed (i.e., the "default" wallet), the migration have been completed successfully, and not have any other copies. This is extremely rare.

Precisely.  I would dare say that under those circumstances (and the age of the default wallet) most people would have a backup.

[goldkingcoiner]

Hopefully the second one, but statistically I think the first one might be more probable.

The fact that I have not had seen any complaints does kind of make it seem nobody lost enough to ragepost yet. So most likely no massive damage has been done. Nobody has lost millions or even thousands (maybe).

To lose access to your wallet, it must be a legacy wallet, its name have not been changed (i.e., the "default" wallet), the migration have been completed successfully, and not have any other copies. This is extremely rare.

Yeah, I guess you might be right.
Bitcoin core wallet is mostly for devs, node runners and privacy maximalists.

Most people don't really use the Bitcoin core wallet.
Normies just want a wallet with the best user experience design and wide range of crypto.  

Not that I care very much for third-party, mixed-crypto wallets since my Trustwallet fiasco. $ 6000 USD gone because of faulty app design and lack of user protection implementations.    

[TryNinja]

Moral of story: backup, backup, backup.

I would never run any process over my wallet if I didn't have a saved file from before the migration. Some people probably would think it's fine since "it's Bitcoin Core, it's safe"... but you can find random bugs everywhere.

[joker_josue]

Moral of story: backup, backup, backup.

Especially when you're doing a software upgrade
All software companies recommend this, before any upgrade. Even when updating the mobile phone this is recommended.

Therefore, the person cannot forget that he is dealing with his money, he has to know how to save it and pro