Read the past · Failures and decisions
When a Lightning Channel Peer Could Make You Overpay
On September 14, 2026, Eclair's developers released version 0.14.3. This was not an ordinary interface update: they described it as security hardening and strongly recommended upgrading because malicious nodes could exploit some of the issues.
EDITORIAL OVERVIEW · Prepared by the project editors from the sources listed below.
An expensive exit from a channel
Eclair manages Lightning channels: opening them, routing payments, and eventually closing them so the final balance returns to Bitcoin's base layer.
During cooperative closing, both sides negotiate a fee. Under certain conditions, the previous fallback could accept an excessive fee proposed by the peer. This did not reveal the owner's keys, but it could deplete the local channel balance. Eclair now rejects proposals that exceed the configured maximum and fall outside the node's local fee range.
An unfinished splice
Splicing changes the size of a Lightning channel without closing it completely. During the operation, old and new channel states temporarily coexist.
If the connection failed at the wrong moment, the node needed to choose a commitment it could actually publish. The fix makes Eclair use the latest commitment whose funding transaction is fully signed. If the new funding transaction confirms first, the node instead closes with the commitment that spends the new output.
Funding created during the payment
The release also strengthens checks for on-the-fly funding, where a channel or liquidity is created while a payment is being routed. Relay fees and CLTV expiry deltas are now checked before forwarding, reducing the chance of accepting unsafe conditions that could lead to a loss.
The automatically estimated fee for opening or splicing a channel is now capped by default at 50 sat/vB.
A security release, not a report of a confirmed theft
The published material does not report a confirmed theft using these bugs. It describes discovered vulnerabilities and defensive changes, not an account of funds already stolen.
Eclair 0.14.3 illustrates an important property of Lightning: fund safety also depends on how unfinished operations, fee limits, and peer proposals are handled. Correct keys cannot repair a rule that agreed to an economically harmful result.
In Lightning, protecting funds depends not only on the seed phrase, but also on the rules used when nodes negotiate.
Sources and verification
Technical material for Lightning node operators. The sources describe vulnerabilities and fixes but do not report a confirmed theft exploiting them.
Unless stated otherwise, the text, conclusions, structure and editorial arrangement were created by the project editors. Facts, quotations and source materials remain attributable to their authors and rights holders.
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