Electrum has rolled out a security update that addresses a defect in its Lightning backups, though certain Bitcoin wallet users must still update their saved backup files.
Because older backups created by wallets utilizing non-deterministic Lightning keys omit critical details, users cannot recover funds from anchor channels—a specific type of Lightning channel—following a remote closure.
As of Oct. 1, version 4.8.2 (released Sept. 11) is still the newest software version displayed on the official Electrum website.
The fix for individual backups incorporates the payment-key data required for users to retrieve their funds from an anchor channel that has been closed by a peer. If this information is missing, the impacted backup cannot generate the key needed to sweep the output—essentially claiming the coins back onto the Bitcoin blockchain.
Which wallets need attention?
According to Electrum’s release notes, two specific criteria must be met: the wallet must utilize non-deterministic Lightning keys, and the backup must involve an anchor channel.
Because non-deterministic keys cannot be regenerated using the wallet’s seed phrase, this warning applies both to individual channel exports and full-wallet backups intended for Lightning recovery.
Lightning wallets that rely on BIP39 seeds or imported extended private keys (xprvs) consistently use non-deterministic Lightning keys. Wallets generated from Electrum seeds behave differently: their Lightning keys are deterministic only if the wallet file was originally generated in version 4.1 or later. Files created in version 4.0.x do not qualify simply because the application has since been updated.
On desktop systems, wallet details specify that the Lightning channels cannot be recovered using the seed, whereas the channel-opening screen on Android displays a warning stating that the channel is unrecoverable from the seed. Operating an anchor channel serves as the second necessary condition for this backup vulnerability.
Additionally, the fix for individual backups disables the option to initiate a remote force-close whenever the backup lacks the ability to sweep the resulting output. This limitation prevents a backup from triggering a closure when it cannot successfully claim the associated funds.
Pull Request 10851 fixes wallet-file exports by preserving a randomly generated Lightning private key that past exports used to drop. Maintainer SomberNight points out that turning Lightning back on within such a backup would create new keys, rendering the older channel-backup records inadequate for spending anchor-channel funds.
Updating the software modifies how backups are generated and interpreted. Consequently, Electrum’s official instructions call for generating brand-new exports, and impacted wallets will show an alert upon startup.
Executing this replacement relies entirely on having kept the initial wallet data required to produce a fresh export. Simply installing the updated software does not ensure the retrieval of key material that was previously lost along with that data.