Electrum users with some Lightning backups need to export them again
Serguey Asael Shinder2 min readA security release of the Electrum Bitcoin wallet from three weeks ago still requires action from some users, CryptoSlate pointed out on 1 October. Electrum 4.8.2, dated 11 September and still the latest release listed on Electrum's website, fixed Lightning channel backups that were missing a key needed to recover funds. The fix applies to backups exported after upgrading; backups already saved stay broken.
According to Electrum's release notes, two conditions must both apply. The wallet must have non-deterministic Lightning keys, and the backup must concern an anchor channel, a Lightning channel type. Such backups, whether individual channel backups or full wallet backups, lacked a key needed to sweep the coins onchain after requesting that the other side force-close the channel. Wallets created from BIP39 seeds or imported extended private keys always have non-deterministic Lightning keys; wallets from Electrum's own seeds have deterministic ones only if the wallet file was created in version 4.1, from March 2021, or later. On desktop the wallet information dialog shows "non-recoverable channels" for affected wallets, and on Android the channel-opening dialog warns that a channel cannot be recovered from seed.
Affected wallets now show a warning on startup, and the notes tell users to export new backups for these channels. Older backups can no longer request a remote force-close, because they could not claim the resulting funds. One of the fixes, pull request 10851, keeps a randomly generated Lightning key that wallet-file exports previously dropped. As CryptoSlate notes, a fresh export depends on still having the original wallet; upgrading cannot restore key material already lost with it. The release also lists fixes for security reports from several researchers and a number of wallet and interface bugs.
Why it matters
Backups are the one part of a wallet nobody tests until they are needed. A fix that changes what future backups contain leaves every earlier copy as it was, so anyone in the affected group should treat the startup warning as an instruction, not information.