Electrum Lightning Fix Comes with a Warning: Old Wallet Backups May Be Incomplete

Electrum's latest security update has fixed a critical flaw in its Lightning backup system, but it also revealed that older Bitcoin wallet backups may be incomplete or even unusable.

The patch, version 4.8.2, was released on September 11 and is still the current release listed on Electrum's official website as of October 1. According to the update notes, the fix addresses an issue with individual channel exports and exported full-wallet backups regarding Lightning recovery.

The problem affects wallets that use non-deterministic Lightning keys, which cannot be recreated from the wallet's seed. This includes Lightning wallets based on BIP39 seeds or imported extended private keys (xprvs), as well as Electrum-seed wallets created before version 4.1. If a backup is made from such a wallet and concerns an anchor channel, it may lack the necessary information to reclaim funds after a remote close.

The update also fixes another issue with wallet-file exports by retaining a randomly generated Lightning private key that was previously deleted. This ensures that future backups will be complete and usable, but affected wallets still need to replace their old backups to avoid potential losses.