PSA: A Foot-Gun in Bitcoin v30

I’m a Bitcoin fanatic. I’m also the guy who loses sleep when Bitcoin software accidentally turns into a foot-gun. So I’m writing this because I’m genuinely worried some of you could get hurt by a Bitcoin Core v30 bug.

Here’s the simple version:

Bitcoin Core v30 has a bug where, in certain situations, trying to “upgrade” an old-style wallet can cause Bitcoin Core to delete your entire wallet folder. Not just the one wallet you were upgrading. The whole folder. That can include other wallets and even backups you kept in that same place.

Why this is a big deal?

In v30, Bitcoin Core stopped supporting the older “legacy” wallet format. So if you upgraded and you still had an older wallet, you basically got pushed into one path forward: migrate (convert) it to the new format.

So the same update that tells you “you need to convert your old wallet” is the one that, if something goes wrong during that conversion, can wipe the folder where your wallets and backups live.

Who this could hit?

People keep saying “it only affects an unnamed legacy wallet” like that’s some rare unicorn. In normal human terms, it often means the classic old default wallet file called wallet.dat. If you’ve been running Bitcoin Core for years, or you set it up long ago and carried it forward, there’s a decent chance that’s what you have.

And “legacy wallet” isn’t ancient history. It was the default until 2022.

How could the conversion “go wrong”?

Yes, something has to fail during the conversion for the worst case to happen. But real life is messy. One example that can trip it: pruning. That’s when your node deletes older blockchain data to save disk space. If you pruned at some point while your wallet wasn’t loaded, it can create a situation where the migration process later stumbles. And when it stumbles, the bug can send it down a “cleanup” path that deletes the whole wallet folder.

If that sounds like a weird chain of events, welcome to production software incidents. It’s always a chain.

What I want you to do (seriously):

Don’t rush to update Bitcoin Core just because a new version dropped. Money software is not a phone app.

If you’re upgrading and you might have an old wallet, treat the migration step like surgery. Slow, careful, planned.

Make a backup outside of Bitcoin Core’s wallet folder. If your “backup” lives in the same folder the bug can delete, it’s not a backup.

If you’re not sure what kind of wallet you have, assume you might be in the blast radius until you verify.

I’m not posting this to score points. I’m posting this because I’ve watched people lose coins to far smaller mistakes than this. Bitcoin rewards paranoia. This is one of those moments where paranoia is just basic competence.

h/t JC Crown for the info.