Eclair Merges Fixes to Stop Nodes Paying Excessive Bitcoin Fees

ACINQ’s Eclair Lightning implementation merged two fixes designed to prevent nodes from paying excessive Bitcoin (BTC) mining fees during collaborative channel funding and transaction construction.

The first change, merged Oct. 2, 2026, limits the fee rate a peer can impose during a replace-by-fee transaction involving a dual-funded channel opening or a splice. Before the fix, a peer could select an arbitrarily high fee rate while contributing nothing, leaving Eclair to cover the mining fee.

“A malicious peer could make us pay mining fees at an arbitrary feerate, while contributing nothing,” Eclair contributor pm47 wrote.

Eclair now rejects peer-initiated replacement transactions above its recommended maximum funding fee rate. The exception applies when the peer purchases liquidity and pays the related fees, or when Eclair contributes no funds.

The second fix, merged Oct. 5, 2026, addresses Eclair-signer mode. In that setup, Bitcoin Core selects coins and constructs transactions, while Eclair retains the keys and signs the transactions.

The updated code calculates the actual fee from transaction inputs and outputs, compares it with the fee reported by Bitcoin Core and applies the fee budget to the verified amount. It also checks that rebuilt funding contributions pay exactly the verified fee and rejects invalid change-output positions.

“We now check that the rebuilt contributions pay exactly the fee we verified on the funded transaction,” pm47 wrote.

Both fixes are merged into Eclair’s master branch. Eclair v0.14.3, released Sept. 14, 2026, is the latest packaged release, but the October fixes are not confirmed as included in a packaged version.

Dual funding allows both parties to contribute to a Lightning channel. Splicing changes an existing on-chain funding transaction without closing the channel, while replace-by-fee allows an unconfirmed transaction to be replaced with one carrying a higher mining fee.

No maximum fee rate, loss amount or affected-node count was identified, and no exploitation was indicated.