Eclair, the Lightning node software developed by ACINQ, has merged two changes designed to protect operators from losing Bitcoin through excessive mining fees during certain channel transactions.
The changes target dual-funded channel openings, channel splicing and Eclair’s signer configuration. In the first case, a peer could previously push a transaction replacement with a higher fee rate while Eclair was contributing funds. In the second, a compromised Bitcoin backend could misrepresent the fee or transaction details even though Eclair retained control of the signing keys.
The repairs were merged into Eclair’s master branch on Oct. 2 and Oct. 5, according to CryptoSlate. However, the project’s release page still identified version 0.14.3, released in September, as the latest packaged release on Oct. 12. The October changes therefore do not by themselves confirm that a new public release containing the fixes was available.
Limiting fee demands during channel funding
One of the changes, pull request #3388, deals with replace-by-fee, or RBF, transactions used in dual-funded channel openings and splicing. These transactions allow a channel transaction to be replaced with another paying a higher fee rate when necessary.
Before the repair, a peer could request an RBF replacement at an arbitrarily high fee rate when Eclair was providing funds to the transaction. Eclair would continue to supply its wallet contribution and pay the fees associated with its inputs, without a maximum fee rate or fee budget on that path.
A malicious peer could therefore cause the Eclair operator to spend a large amount of Bitcoin on fees while contributing nothing toward that cost. The Bitcoin would not be sent to the attacker’s address; instead, the excess would be paid to miners as a transaction fee. The risk was that the contributing node’s funds could be consumed by the fee requirement.
The merged repair rejects fee-bump attempts above the maximum funding fee rate that Eclair recommends to its peer. The limit does not apply in two situations described in the change: when the peer purchases liquidity and pays the fees for Eclair’s inputs, or when Eclair contributes no funds to the transaction. In those cases, Eclair does not bear the specific cost addressed by the new restriction.
Verifying fees when the backend builds transactions
The second change, pull request #3390, applies to Eclair-signer mode. In this setup, Bitcoin Core’s bitcoind backend selects coins and constructs transactions, while Eclair keeps the private keys and signs the resulting transactions.
Retaining the keys is not enough to protect against every backend-related transaction risk. A compromised backend could claim that a transaction stayed within its fee budget while building one that actually paid more. It could, for example, omit a change output.
In Bitcoin transactions, the value of the inputs must be allocated either to outputs or to the miner fee. If a change output is removed, the unallocated amount becomes part of the fee. That means a manipulated transaction could spend additional funds without directing those funds to an attacker’s address.
The repair calculates the actual fee from the value of the coins being spent. Those values are retrieved by transaction ID to authenticate the inputs. When a fee budget is provided, Eclair checks that the backend’s reported fee matches the verified calculation and then applies the budget to the actual fee rather than relying only on the backend’s description.
The change also verifies that rebuilt Eclair contributions pay the same fee as the previously checked transaction and rejects invalid positions for change outputs. Together, these checks are intended to close the gap between the transaction a backend reports and the transaction Eclair would actually sign.
What operators should know, and the market picture
The two repairs concern different configurations: peer-selected fee replacements during dual funding and splicing, and transaction verification in signer mode. They are separate from the cooperative-closing fee issue discussed in CryptoSlate’s September report and from the restart-related denial-of-service problems covered on Oct. 2.
Because the fixes were merged after the latest listed packaged release, operators need to determine whether their installed Eclair build includes the October changes. The source material does not confirm that a release incorporating both repairs had been published by Oct. 12.
Moneyiar market data at 10:09 on Oct. 13, 2026, showed Bitcoin at $83,508.35, up 0.12% over 24 hours but down 2.90% over seven days. Rootstock Infrastructure Framework (RIF) was $0.0818481, down 2.44% in 24 hours and 0.91% over seven days. Light (LIGHT) stood at $0.1672899542, up 1.73% over 24 hours and down 9.40% over seven days; its supplied reading was timestamped 02:53 on Sept. 14, 2026. FUNToken (FUN) was $0.0086986786, down 0.93% over 24 hours and up 7.28% over seven days.
