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Low 44 Bitcoin

Gate interactive commitment_signed on user approval during reestablish

Public commit record

What the developer wrote

Authored by Wilmer Paulino

73/100 · Adequate
Gate interactive commitment_signed on user approval during reestablish

Interactive funding transactions must be approved by the user via
`ChannelManager::funding_transaction_signed` prior to exchanging
signatures for it. This ensures the user is able to cancel up until the
very last point throughout the handshake. When this was done in 83b2d3e,
we forgot the cover the reestablish cases, which we do here.
✓ Specific, descriptive subject✓ Names a concrete action or component✓ Provides detailed explanatory context
The short version

What changed, and why it matters

This patch fixes a logic gap in Lightning Dev Kit's interactive splicing handshake. During a channel reconnection, the code could re-send a commitment signature for a new funding transaction before the user had actually approved and provided their own transaction signatures. The fix gates that retransmission so it only happens after the user calls funding_transaction_signed, preserving the intended 'cancel up to the last moment' behavior.

Recommended action

Review whether any other reestablish or retransmission paths for interactive funding can emit commitment_signed or tx_signatures before holder approval. Ensure the new has_holder_witnesses gate is applied consistently across all interactive-tx flows. Consider adding tests for the abort/cancel path and for the non-initiator side.

Security signals we found

01

Missing authorization gate in protocol state machine

02

Premature cryptographic commitment retransmission on reconnection

03

User-intended cancellation window bypassed

04

Regression test added for reestablish path

Risk score

Why this scored 44/100

Our methodology →
Potential impact 12/30
Exploitability 8/25
Stealth signal 7/15
Affected reach 6/15
Confidence 7/10
Evidence quality 4/5
Human-validated context

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