LDK Patch Blocks Probe Linking Private Lightning Channels to Bitcoin Funding

The Lightning Development Kit (LDK) merged a fix that blocks a peer connected to both ends of an unannounced Lightning channel from using onion-message forwarding to link the channel to its Bitcoin (BTC) funding output.

The change was merged Oct. 25 at 4:25 p.m. ET (20:25 UTC). It rejects an unannounced channel’s real short channel ID (SCID) during onion-message forwarding while allowing the channel’s outbound alias.

Once funding for a private channel was confirmed, LDK could look up its real SCID. A peer connected to both endpoints could try a guessed SCID in an onion message and check whether the message returned. A match could link the channel’s nodes to the funding output’s location on the Bitcoin blockchain.

A real SCID identifies the funding output’s block height, transaction position in that block and output position in the transaction. An unannounced channel is not shared through network gossip, but its funding output remains on-chain.

The change applies to onion-message forwarding and does not establish that every Lightning payment route had the same lookup behavior. LDK version 0.2.7 is dated Oct. 1, before the merge. The merge does not establish when releases, wallets or nodes will include the fix.