Allow remote `dust_limit_satoshis` up to 5000 sats (#3227)
What the developer wrote
Authored by Bastien Teinturier
Allow remote `dust_limit_satoshis` up to 5000 sats (#3227)
Set allow remote `dust_limit_satoshis` up to 5000 sats, which means that
HTLC outputs should be claimable at feerates lower than `25 sat/kw`.
Given that our default `dust-tolerance` is set to 50 000 sats, this
allows at least 10 pending dust HTLCs before we start failing dust HTLCs
back instead of relaying them.
What changed, and why it matters
This commit lowers the maximum dust-limit Eclair will accept from a remote Lightning peer from 10,000 satoshis to 5,000 satoshis. Dust limits determine which tiny channel outputs can be created on-chain. The change is framed as a defensive tightening: with Eclair's default dust tolerance of 50,000 sats, it still allows at least 10 tiny HTLCs to be pending before the node stops relaying them. The commit message itself describes the change in security-relevant terms (preventing uneconomical on-chain HTLC claims), but the diff is a single configuration value change and does not fix an obvious, exploitable bug.
Treat as a minor defensive configuration hardening. Review whether local node operators should override this value, and monitor for follow-up commits or BOLTs discussion that clarify the security rationale. No urgent patching is indicated by the commit alone.
Security signals we found
Configuration change affecting channel funding/HTLC dust policy
Commit message explicitly discusses on-chain claimability and dust HTLC relay behavior
Reduces accepted remote dust limit, a defensive tightening
No code logic change; relies on existing enforcement of max-remote-dust-limit-satoshis
No CVE, advisory, researcher credit, or vendor security disclosure referenced in commit
Evidence from the diff
The patch changes max-remote-dust-limit-satoshis in reference.conf from 10000 to 5000. In anchor-output Lightning channels, HTLC outputs below the dust limit are not emitted as separate on-chain outputs; their value is instead added to the commitment transaction fee (trimmed). A higher remote dust limit means more HTLCs can be forced to be trimmed, which can change fee-bumping economics and potentially affect the ability to claim funds on-chain. The commit message states the goal is to ensure HTLC outputs remain claimable at feerates below 25 sat/kw. This is a policy tightening, not a code-level vulnerability fix.
Changed components
eclair-core/src/main/resources/reference.confEclair Lightning channel dust-limit policyAnchor output channel HTLC trimming behaviorInspect captured patch +1 / −1
diff --git a/eclair-core/src/main/resources/reference.conf b/eclair-core/src/main/resources/reference.conf
index 64f6c89..5391654 100644
--- a/eclair-core/src/main/resources/reference.conf
+++ b/eclair-core/src/main/resources/reference.conf
@@ -120,7 +120,7 @@ eclair {
dust-limit-satoshis = 546
// Starting with anchor outputs channels, the on-chain feerate is not taken into account when trimming outputs.
// We must thus use a high enough dust limit to ensure that the outputs can economically be spent on-chain.
- max-remote-dust-limit-satoshis = 10000
+ max-remote-dust-limit-satoshis = 5000
htlc-minimum-msat = 1
// The following parameters apply to each HTLC direction (incoming or outgoing), which means that the maximum amount in flight will be at most twice what is set here.
// Note that our peer may use a lower value than ours, which would reduce the maximum amount in flight.
Why this scored 37/100
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