Bitcoin Core wallet migration bug in versions 30.0 and 30.1

[LFC_Bitcoin]

@BitcoinNewsCom
NEW: Bitcoin Core developers issues a warning about a wallet migration bug in versions 30.0 and 30.1 that can cause permanent loss of funds for users migrating from very old Bitcoin Core wallets that were never renamed or upgraded.

https://x.com/bitcoinnewscom/status/2008515895962804351

[LoyceV]

"If those wallets aren't backed up"

Imagine running a very old legacy wallet for all those years without having a backup, and then finally deciding to upgrade your only version of your wallet. I have no doubt those people still exist, but damn!

[Amphenomenon]

"If those wallets aren't backed up"

Imagine running a very old legacy wallet for all those years without having a backup, and then finally deciding to upgrade your only version of your wallet. I have no doubt those people still exist, but damn!

I hope these reach as many as possible before they make regretful decision, but why will someone literally do something like this , I guess some might have backed up theirs before but lost it unknowingly to them.

[LFC_Bitcoin]

"If those wallets aren't backed up"

Imagine running a very old legacy wallet for all those years without having a backup, and then finally deciding to upgrade your only version of your wallet. I have no doubt those people still exist, but damn!

Yeah I have always backed mine up, multiple times, I have to be honest. I moved all my Legacy address Bitcoin to Segwit a couple of years ago.

I think the next time we will have to move coins for something other than selling is if Quantum becomes an actual threat. I haven’t read up in too much detail but I believe there will be Quantum Proof addresses or a patch to avoid any potential losses.

That’s a discussion for another day any way but I thought it was the right thing to post this here after seeing it, even if like you said, only a few people are careless enough to not have backups.

[Cookdata]

"If those wallets aren't backed up"

Imagine running a very old legacy wallet for all those years without having a backup, and then finally deciding to upgrade your only version of your wallet. I have no doubt those people still exist, but damn!

I hope these reach as many as possible before they make regretful decision, but why will someone literally do something like this , I guess some might have backed up theirs before but lost it unknowingly to them.

It's been two weeks since the reports were posted on Github https://github.com/bitcoin/bitcoin/issues/34128#issue-3750246491; there could be more damage or maybe less. I think an old legacy user ought to know the importance of wallet back up than anyone.

If you know the process, the wallet migration, wallet back up will be the first thing that will comes to your mind before you even start.

[LoyceV]

If you know the process, the wallet migration, wallet back up will be the first thing that will comes to your mind before you even start.

Why doesn't Bitcoin Core do this by default? Instead of overwriting your wallet.dat, shouldn't the default behaviour be to rename it to wallet.backup20260501.dat before creating a new wallet.dat?

[achow101]

If you know the process, the wallet migration, wallet back up will be the first thing that will comes to your mind before you even start.

Why doesn't Bitcoin Core do this by default? Instead of overwriting your wallet.dat, shouldn't the default behaviour be to rename it to wallet.backup20260501.dat before creating a new wallet.dat?

It does.

The problem is that the backups are stored in a directory that is accidentally deleted by the bug as well. Obviously this is a major bug and it took a little while to figure out the scope of the issue.

[satscraper]

"If those wallets aren't backed up"

Imagine running a very old legacy wallet for all those years without having a backup, and then finally deciding to upgrade your only version of your wallet. I have no doubt those people still exist, but damn!

Terrible prospect, I can’t even imagine this with Bitcoin Core.

Luckily, I use Bitcoin Core ^30.0 solely as a node, not as the wallet. My stash is controlled by hardware wallet, namely Passport Core. But the chance that someone could be caught by this bug ^{if they haven’t been already} isn’t zero. Brrrr.

[LFC_Bitcoin]

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

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

[LoyceV]

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

What are the odds: this pretty much describes my current wallet! But I have no intention to upgrade yet, I like the possibility of easily importing a private key when needed. And of course I have backups.

[LFC_Bitcoin]

What are the odds: this pretty much describes my current wallet! But I have no intention to upgrade yet, I like the possibility of easily importing a private key when needed. And of course I have backups.

I don’t like to upgrade very often but I did upgrade to 29.0 not long back because of all the Knots nonsense going on. I just wanted to make sure I was pre 30.0 as I had a feeling there could be problems.

As for importprivkey, I have ‘t done that for a very long time but literally only became aware a few days ago after reading on here that the process has changed to a slightly more techie way of doing it. I don’t know why that was messed with, it was fine as it was.

[nc50lc]

Luckily, I'm not affected by this since I'm still using v29.0.

Good thing that the previous migration process of v29 and below isn't affected since I've used it a few times and it never failed,
Or is it?

But I have no intention to upgrade yet, I like the possibility of easily importing a private key when needed.

I'm not persuading you to upgrade but it should be easy for you to learn the new importdescriptors command to import WIFs wrapped as single-key descriptors.
Once you get the hang of it, it should be simple enough to do within a minute (excluding rescan of course)

[LoyceV]

it should be easy for you to learn the new importdescriptors command to import WIFs wrapped as single-key descriptors.

I've seen your posts explaining it, and I can do it, but it feels so pointless to upgrade to something that makes a basic task 30 times more work. I'll upgrade after they make a single command to import them

[achow101]

Good thing that the previous migration process of v29 and below isn't affected since I've used it a few times and it never failed,
Or is it?

This particular bug is not reachable on 29.x and earlier.