Eclair tightens Bitcoin funding rules after unconfirmed inputs put Lightning payments at risk
Bitcoin Lightning developer ACINQ has released an urgent security update for Eclair after identifying flaws that could allow malicious nodes to manipulate unconfirmed channel funding transactions.
The October 27 release requires confirmed peer inputs for splices by default and improves recovery when a channel must close with funding still pending. Senior Reporter CryptoSlate reported that the update addresses vulnerabilities that could jeopardize pending Bitcoin payments and fund recovery.
Security vulnerability identified
ACINQ has urged node operators to upgrade after fixing security weaknesses that malicious peers could exploit. The company released Eclair version 0.14.6 on Oct. 27, introducing stricter transaction requirements and recovery mechanisms to prevent manipulated channel funding from jeopardizing pending payments.
We highly recommend upgrading, as some of these issues can be exploited by malicious nodes.
Flaw in channel funding
The warning centers on a weakness in how Lightning channels handle funding changes before the underlying Bitcoin transactions are confirmed. Lightning allows users to transfer Bitcoin through payment channels without recording every transaction on the blockchain. Operators can also add or withdraw liquidity from existing channels through a process known as splicing.
ACINQ's release documentation warns that accepting unconfirmed funding inputs from another node creates an opportunity for manipulation. A malicious peer could double-spend an unconfirmed transaction after signing a splice, invalidating the funding arrangement that supports the channel.
New security measures implemented
The update introduces a new security setting that requires confirmed inputs from peers before they can contribute funds to channel splices. Enabled by default, the protection also prevents operators from building additional splices on top of unconfirmed funding changes, reducing opportunities for malicious peers to undermine settlement.
The developers also strengthened the software's response when a channel must close while a funding transaction remains unconfirmed. Under the revised settlement logic, Eclair selects a commitment transaction backed by funding that its Bitcoin Core backend recognizes, reverting to the latest confirmed funding state when necessary.
Recovery mechanisms improved
The new logic recognizes transactions that miners confirm after Eclair has stopped tracking them as its preferred settlement route. Previously, the software could misidentify such a transaction as belonging to the counterparty, potentially failing to claim funds and pending payment outputs that remained recoverable.
The release credits security researcher Erick Cestari with responsibly disclosing issues addressed by the update. Operators running older Eclair versions have been advised to install the patch and retain the new confirmed-input safeguard.
Related
