Lightning apps using unpatched LDK risk Bitcoin theft from a reconnect lie

A commitment transaction represents a channel's agreed state and can be used to settle it on Bitcoin's blockchain. In the scenario described in PR 5057, the newly signed transaction was not recorded by LDK's channel monitor, the component tracking the channel's on-chain claims.

That gap could turn a forwarded payment into a loss. The malicious sender could confirm the transaction on-chain and let the payment settle with the next recipient. It could then reclaim the incoming payment contract when it expired, even though the forwarding node knew the secret normally used to claim payment.

The forwarding application would have paid downstream without recovering the corresponding incoming funds. The fix permits retransmission only while the peer's acknowledgment remains outstanding and force-closes the channel when the peer claims an already-acknowledged update was missed.

Alongside the LDK reconnect fix, version 0.2.7 addresses a different theft path involving LSPS2 just-in-time payments, where a liquidity service opens a channel as part of handling a payment.

An intercepted payment could misrepresent its amount, causing the service to open a channel and forward more Bitcoin than the incoming payment supplied. The service would cover the difference from its own funds. PR 5042 addresses that amount check.