Critical Bitcoin Lightning bugs exposed nodes to fund theft and restart failure

Lightning Development Kit, a toolkit for building Bitcoin Lightning applications, released v0.2.6 on Sept. 9 with fixes for bugs that could divert small amounts of a node’s funds or prevent saved channel state from loading.

LDK packages a Lightning implementation as a software development kit for uses including mobile wallets and payment-service infrastructure. The update gives developers maintaining affected applications fixes for both a financial risk and a condition that can disrupt normal node restarts.

A splice lets a node add funds to or remove funds from an existing payment channel. LDK’s API documentation describes this as spending the channel’s funding output and replacing it with a new one. In practical terms, it changes the money committed to the channel through a replacement funding transaction.

That transaction has costs shared between the participants. The initiating node pays fees for specified common parts, along with its own contributed inputs and outputs. The fee calculation therefore affects how much of the node’s money pays for the operation.

The splice flaw could let a malicious peer cause excess fee allocation, with the excess going to that peer’s output. The release describes a small amount of funds at risk when a node initiates a splice, without specifying a numerical ceiling.